The Umbraco backoffice consists of sections (sometimes referred to as applications) which contain Trees.

Each section is identified by its name in the top navigation ribbon of the Umbraco Backoffice.

For example, when you load the backoffice, you'll see that the 'Content' section contains one tree: the content tree. Meanwhile, the 'Settings' section contains a number of trees such as Stylesheets, Document Types, Media Types, etc...

You can create your own sections and trees to extend Umbraco.

Sections

Describes Umbraco Sections, configuration and APIs.

Trees

Describes Umbraco Trees, configuration, APIs and events.

Searchable Trees (ISearchableTree)

Explains how to customise the backoffice search of a Section Tree.

The Umbraco backoffice consists of Sections, also referred to as Applications, which contain Trees.

Each section is shown in the top navigation ribbon of the Umbraco Backoffice.

Create a Custom Section

To create a new custom section in your Umbraco backoffice, the first thing you have to do is create a new folder inside /App_Plugins. We will call it MyFavouriteThings.

Next we need to create a manifest where we'll include some basic configuration for our new section.

Registering a Custom Section

There are two approaches to registering a custom section to appear in the Umbraco Backoffice:

Registering with package.manifest

Create a new file in the /App_Plugins/MyFavouriteThings/ folder and name it package.manifest. In this new file, copy the code snippet below and save it.

{
    "sections": [
        {
            "alias": "myFavouriteThings",
            "name": "My Favourite Things"
        }
    ]
}

This would create a new section in your Umbraco backoffice called 'My Favourite Things'.

When registering your section this way, it is added to the end of the collection of sections. But as more package.manifest files may do the same, the order of the additional sections depends on the order of which the package.manifest files are loaded. Registering your section this way doesn't allow further control of its order.

Registering with C# Type

By creating a C# class that implements ISection from Umbraco.Cms.Core.Sections:

using Umbraco.Cms.Core.Sections;

namespace My.Website.Sections;

public class MyFavouriteThingsSection : ISection
{
    public string Alias => "myFavouriteThings";

    public string Name => "My Favourite Things";
}

For your C# type to be discovered by Umbraco at application start up, it needs to be appended to the SectionCollectionBuilder.

You can achieve this by creating a Composer and call the Append method:

using Umbraco.Cms.Core.Composing;

namespace My.Website.Sections;

public class SectionComposer : IComposer
{
    public void Compose(IUmbracoBuilder builder)
    {
        builder.Sections().Append<MyFavouriteThingsSection>();
    }
}

This would also create a new section called 'My Favourite Things' in your Umbraco Backoffice.

Similar to registering the section via a package.manifest file, the Append<> method will add the section to the end of the list of sections.

If you wish to control the order of your section a bit more, you can use some of the other methods on SectionsCollectionBuilder. For instance, you can add your section at a specific index:

builder.Sections().Insert<MyFavouriteThingsSection>(2);

Or before or after an existing section:

builder.Sections().InsertBefore<SettingsSection, MyFavouriteThingsSection>();

builder.Sections().InsertAfter<SettingsSection, MyFavouriteThingsSection>();

The final order of the sections is down to the order of which the composers are executed. For instance, two composers may add a new section before SettingsSection, in which case the latter will add its section between the section of the first composer and SettingsSection.

Why can't I see my new Custom Section?

You will also need to allow your current Umbraco User group access to this new Custom Section via the backoffice! (you will need to logout and back in again to see the change)

Adding a Language Translation (get rid of the square brackets)

When your new custom section appears, you'll notice only the section 'Alias' is displayed inside square brackets. This is because Umbraco caters for Multiple Languages in the backoffice, and is looking for a translation file for the current backoffice culture, containing a translation key for your custom section alias.

Create a /lang folder in the folder where you are creating the implementation for your custom section. If you do not have one already, create a /lang folder within the folder where you are creating the implementation for your custom section, eg. /App_Plugins/MyFavouriteThings/lang/.

It is worth knowing that the /lang folder does not have to be directly in the MyFavouriteThings folder, it can be nested deeper if you need it to be. The only requirement is that the folder is called lang. E.g. ~/App_Plugins/MyFavouriteThings/Some/Another/Lang/.

Inside this folder create a file called en-us.xml. This is the 'default' fallback language translation file. Add the following definition:

<?xml version="1.0" encoding="utf-8" standalone="yes"?>
<language alias="en" intName="English (US)" localName="English (US)" lcid="" culture="en-US">
  <area alias="sections">
    <key alias="myFavouriteThings">My Favourite Things</key>
  </area>
</language>

Recycle the application pool, and the square brackets will be gone, and your section will have the title 'My Favourite Things'.

You can add custom language translation keys in this file for providing translated versions of text used throughout your custom section/tree implementation.

To provide translations in other languages, duplicate the en-us.xml file in the /lang folder and rename it to match the lang/culture combination of your newly supported language. Update the contents of the language element attributes, and provide a translation for each 'language translation key'.

You will need to recycle the application pool, to see changes to the language translation files reflected in the backoffice.

Now create a custom tree to load in your custom section!

Items in an Umbraco Tree can have associated Actions. The actions visible to the currently logged in user can be controlled via User Permissions.

You can set a User's permissions for each item in the Umbraco Content tree from the User Section of the Umbraco Backoffice.

If you are developing a custom section, or a custom Dashboard, you might want to display some different options based on a User's permission set on a particular item.

For example, on a custom dashboard you might add a quick 'Create a Blog Post' button for an editor, but only if that editor has permissions to create a blog post. You could create some sort of API endpoint, to call from your AngularJS controller, that in turn uses the UserService to return the current user's permissions. Then you can see whether they have the required permission to 'create' within the site's blog section.

bool canCreateBlogs = false;
var user = _userService.GetByEmail(email);
var userPermissionsForBlog = _userService.GetPermissions(user, blogId);
foreach (var permission in userPermissionsForBlog)
{
    if (permission.AssignedPermissions.Contains("C"))
    {
        canCreateBlogs = true;
    }
}

But how to know which letter corresponds to which Tree Action?

Each tree action in Umbraco implements the IAction interface, and each Action has a corresponding 'Letter', and a boolean value describing whether permissions can be assigned for an action.

public interface IAction : IDiscoverable
{
    char Letter {get;}
    bool ShowInNotifier {get;}
    bool CanBePermissionAssigned {get;}
    string Icon {get;}
    string Alias {get;}
    string JsFunctionName {get;}
    /// <summary>
    /// A path to a supporting JavaScript file for the IAction. A script tag will be rendered out with the reference to the  JavaScript file.
    /// </summary>
    string JsSource {get;}
}

When you pull back the AssignedPermissions for a user on a particular item, it is these letters that indicate which actions the User is permitted to perform in the context of the tree item.

User Permission Codes

Here is a list of the tree actions and associated user permission codes shipped by Umbraco CMS and add-on projects (such as Umbraco Deploy), as well as those used by some community packages.

If building a package or adding custom tree actions to your solution, it's important to pick a permission letter that doesn't clash with one of these.

If you have created a package using a custom tree action, please consider providing an update to this documentation page via a PR to the documentation repository, such that other developers can discover and avoid using the same permission letter.

Note: up until Umbraco Deploy 9.2.0, the letter "N" was used for the "Queue For Transfer" action. In 9.2.1 it was changed to be "T", to avoid clashing with the letter selected for the Umbraco CMS "Notify" action, introduced in CMS version 8.18.

This section describes how to work with and create trees with Umbraco APIs.

Creating trees

To Create a Tree in a section of the Umbraco backoffice, you need to take several steps:

Create a TreeController class in C#. A new controller which inherits from the abstract Umbraco.Cms.Web.BackOffice.Trees.TreeController*` class and provides an implementation for two abstract methods:

• GetTreeNodes (returns a TreeNodeCollection) - Responsible for rendering the content of the tree structure;

• GetMenuForNode (returns a MenuItemCollection) - Responsible for returning the menu structure to use for a particular node within a tree.

You will need to add a constructor as TreeController requires this. See full code snippet in the "Implementing the Tree" section below.

The Tree attribute used to decorate the TreeController has multiple properties.

• SectionAlias - Alias of the section in which the tree appears

• TreeAlias - Alias of the tree

• TreeTitle - The title of the tree

• TreeGroup - The tree group, the tree belongs to

• SortOrder - Sort order of the tree

For example:

[Tree("settings", "favouriteThingsAlias", TreeTitle = "Favourite Things Name", TreeGroup="favouritesGroup", SortOrder=5)]
public class FavouriteThingsTreeController : TreeController
{ }

The example above would register a custom tree with a title 'Favourite Things Name' in the Settings section of Umbraco, inside a custom group called 'Favourites'.

Tree Groups

Tree Groups enable you to group trees in a section. You provide the alias of the Tree Group name, you wish to add your tree to - see Constants.Trees.Groups for a list of existing group alias. An example of tree groups in the backoffice would be the Settings tree group and the Templating tree group in the Settings section.

If you add your own alias, you'll need to add a translation key. This can be done by adding a language file to a lang folder with your application folder in App_Plugins: App_Plugins/favouriteThings/lang/en-us.xml. This will avoid the alias appearing as the header in [square brackets].

The language file should contain the following XML:

<language>
  <area alias="treeHeaders">
    <key alias="favouritesGroup">Favourites</key>
  </area>
</language>

Customising the Root Tree Node

The first node in the tree is referred to as the Root Node. You can customise the Root Node by overriding the abstract CreateRootNode method. You can assign a custom icon to the Root Node. You can also specify a custom URL route path in the backoffice to use with your custom tree. The method can be useful if your section has a single node (single page app).

See Also: How to create your own custom section

Implementing the Tree

using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.Mvc;
using Umbraco.Cms.Core;
using Umbraco.Cms.Core.Actions;
using Umbraco.Cms.Core.Events;
using Umbraco.Cms.Core.Models.Trees;
using Umbraco.Cms.Core.Services;
using Umbraco.Cms.Core.Trees;
using Umbraco.Cms.Web.BackOffice.Trees;
using Umbraco.Extensions;

namespace My.Website.Trees
{
    [Tree("settings", "favouriteThingsAlias", TreeTitle = "Favourite Things Name", TreeGroup = "favouritesGroup", SortOrder = 5)]
    public class FavouriteThingsTreeController : TreeController
    {

        private readonly IMenuItemCollectionFactory _menuItemCollectionFactory;

        public FavouriteThingsTreeController(ILocalizedTextService localizedTextService,
            UmbracoApiControllerTypeCollection umbracoApiControllerTypeCollection,
            IMenuItemCollectionFactory menuItemCollectionFactory,
            IEventAggregator eventAggregator)
            : base(localizedTextService, umbracoApiControllerTypeCollection, eventAggregator)
        {
            _menuItemCollectionFactory = menuItemCollectionFactory ?? throw new ArgumentNullException(nameof(menuItemCollectionFactory));
        }

        protected override ActionResult<TreeNodeCollection> GetTreeNodes(string id, FormCollection queryStrings)
        {
            var nodes = new TreeNodeCollection();

            // check if we're rendering the root node's children
            if (id == Constants.System.Root.ToInvariantString())
            {
                // you can get your custom nodes from anywhere, and they can represent anything...
                Dictionary<int, string> favouriteThings = new Dictionary<int, string>();
                favouriteThings.Add(1, "Raindrops on Roses");
                favouriteThings.Add(2, "Whiskers on Kittens");
                favouriteThings.Add(3, "Skys full of Stars");
                favouriteThings.Add(4, "Warm Woolen Mittens");
                favouriteThings.Add(5, "Cream coloured Unicorns");
                favouriteThings.Add(6, "Schnitzel with Noodles");

                // loop through our favourite things and create a tree item for each one
                foreach (var thing in favouriteThings)
                {
                    // add each node to the tree collection using the base CreateTreeNode method
                    // it has several overloads, using here unique Id of tree item,
                    // -1 is the Id of the parent node to create, eg the root of this tree is -1 by convention
                    // - the querystring collection passed into this route
                    // - the name of the tree node
                    // - css class of icon to display for the node
                    // - and whether the item has child nodes
                    var node = CreateTreeNode(thing.Key.ToString(), "-1", queryStrings, thing.Value, "icon-presentation", false);
                    nodes.Add(node);
                }
            }

            return nodes;
        }

        protected override ActionResult<MenuItemCollection> GetMenuForNode(string id, FormCollection queryStrings)
        {
            // create a Menu Item Collection to return so people can interact with the nodes in your tree
            var menu = _menuItemCollectionFactory.Create();

            if (id == Constants.System.Root.ToInvariantString())
            {
                // root actions, perhaps users can create new items in this tree, or perhaps it's not a content tree, it might be a read only tree, or each node item might represent something entirely different...
                // add your menu item actions or custom ActionMenuItems
                menu.Items.Add(new CreateChildEntity(LocalizedTextService));
                // add refresh menu item (note no dialog)
                menu.Items.Add(new RefreshNode(LocalizedTextService, true));
            }
            else
            {
                // add a delete action to each individual item
                menu.Items.Add<ActionDelete>(LocalizedTextService, true, opensDialog: true);
            }

            return menu;
        }

        protected override ActionResult<TreeNode?> CreateRootNode(FormCollection queryStrings)
        {
            var rootResult = base.CreateRootNode(queryStrings);
            if (!(rootResult.Result is null))
            {
                return rootResult;
            }

            var root = rootResult.Value;

            // set the icon
            root.Icon = "icon-hearts";
            // could be set to false for a custom tree with a single node.
            root.HasChildren = true;
            //url for menu
            root.MenuUrl = null;

            return root;
        }
    }
}

Responding to Tree Actions

The actions on items in an Umbraco Tree will trigger a request to load an AngularJS view, with a name corresponding to the name of the action, from a subfolder of the views folder matching the name of the 'customTreeAlias'.

Clicking on one of the 'Favourite Things' in the custom tree example will load an edit.html view from the folder: /views/favouriteThingsAlias/edit.html. The 'Delete' menu item would also load a view from: /views/favouriteThingsAlias/delete.html

When creating a custom tree as part of a Umbraco package, it is recommended to change the location of the default folder. It should be changed to the App_Plugins folder. You achieve this by decorating your MVC TreeController with the PluginController attribute.

@using Umbraco.Cms.Web.Common.Attributes;

[Tree("settings", "favouriteThingsAlias", TreeTitle = "Favourite Things Name")]
[PluginController("favouriteThings")]
public class FavouriteThingsTreeController : TreeController
{ }

The edit view in the example would now be loaded from the location: /App_Plugins/favouriteThings/backoffice/favouriteThingsAlias/edit.html

Providing functionality in your Tree Action Views

You can instruct the Umbraco backoffice to load additional JavaScript resources (eg. angularJS controllers) to use in conjunction with your 'tree action views' by adding a package.manifest file in the same folder location as your views.

For example...

{
    "javascript": [
        "~/App_Plugins/favouriteThings/favouriteThings.resource.js",
        "~/App_Plugins/favouriteThings/backoffice/favouriteThingsAlias/edit.controller.js",
        "~/App_Plugins/favouriteThings/backoffice/favouriteThingsAlias/delete.controller.js"
    ]
}

...this manifest would load files for two controllers to work with the edit and delete views and a general resource file, perhaps containing code to retrieve, create, edit and delete 'favourite things' from some external non-Umbraco API.

Our Tree Action View would then be wired to the loaded controller using the ng-controller attribute. The delete view would perhaps the delete view look a little bit like this:

<div class="umb-dialog umb-pane" ng-controller="Our.Umbraco.FavouriteThings.DeleteController">
    <div class="umb-dialog-body">
        <p class="umb-abstract">
            Are you sure you want to delete this favourite thing: <strong>{{currentNode.name}}</strong> ?
        </p>
        <umb-confirm on-confirm="performDelete" on-cancel="cancel">
        </umb-confirm>
    </div>
</div>

see Tree Actions for a list of tree ActionMenuItems and IActions

Single Node Trees / Customising the Root Node Action

It is possible to create 'trees' consisting of only a single node - perhaps to provide an area to control some settings or a placeholder for a single page backoffice app. See the LogViewer in the settings section for a good example. (or as in the case of the 'settings/content templates' tree, it's possible to have a custom view for the root node as an 'introduction' page to the tree).

In both scenarios you need to override the CreateRootNode method for the custom tree.

[Tree("settings", "favouritistThingsAlias", TreeTitle = "Favourite Thing", TreeGroup = "favoritesGroup", SortOrder = 5)]
[PluginController("favouriteThing")]
public class FavouritistThingsTreeController : TreeController
{ }

You can override the CreateRootNode method to set the 'RoutePath' to where the single page application will live (or introduction page). Setting HasChildren to false will result in a Single Node Tree.

protected override ActionResult<TreeNode> CreateRootNode(FormCollection queryStrings)
{
    var rootResult = base.CreateRootNode(queryStrings);
    if (!(rootResult.Result is null))
    {
        return rootResult;
    }

    var root = rootResult.Value;

    //optionally setting a routepath would allow you to load in a custom UI instead of the usual behaviour for a tree
    root.RoutePath = string.Format("{0}/{1}/{2}", Constants.Applications.Settings, "favouritistThingsAlias", "overview");
    // set the icon
    root.Icon = "icon-hearts";
    // set to false for a custom tree with a single node.
    root.HasChildren = false;
    //url for menu
    root.MenuUrl = null;

    return root;
}

The RoutePath should be in the format of: section/treeAlias/method. As our example controller uses the PluginController attribute, clicking the root node would now request /App_Plugins/favouriteThing/backoffice/favouritistThingsAlias/overview.html. If you are not using the PluginController attribute, then the request would be to /umbraco/views/favouritistThingsAlias/overview.html.

Full Width App - IsSingleNodeTree

It's possible to make your single node tree app stretch across the full screen of the backoffice (no navigation tree) - see Packages section for an example. To achieve this add an additional attribute IsSingleNodeTree, in the Tree attribute for the custom controller.

[Tree("settings", "favouritistThingsAlias", IsSingleNodeTree = true, TreeTitle = "Favourite Thing", TreeGroup = "favoritesGroup", SortOrder = 5)]
[PluginController("favouriteThing")]
public class FavouritistThingsTreeController : TreeController
{ }

Tree notifications

All tree notications are defined in the namespace Umbraco.Cms.Core.Notifications.

For more information about registering and using notifications see Notifications

RootNodeRenderingNotification

The RootNodeRenderingNotification is published whenever a tree's root node is created.

Members:

• TreeNode Node

• FormCollection QueryString

• string TreeAlias

Usage:

public void Handle(RootNodeRenderingNotification notification)
{
    // normally you will want to target a specific tree, this can be done by checking the tree alias
    if (notification.TreeAlias.Equals("content"))
    {
        notification.Node.Name = "My new title";
    }
}

TreeNodesRenderingNotification

The TreeNodesRenderingNotification is published whenever a list of child nodes are created.

Members:

• TreeNodeCollection Nodes

• FormCollection QueryString

• string TreeAlias

Usage:

using Umbraco.Cms.Core.Security;

public class TreeNotificationHandler :INotificationHandler<TreeNodesRenderingNotification>
{
    private readonly IBackOfficeSecurityAccessor _backOfficeSecurityAccessor;

    public TreeNotificationHandler(IBackOfficeSecurityAccessor backOfficeSecurityAccessor)
    {
        _backOfficeSecurityAccessor = backOfficeSecurityAccessor;
    }

    public void Handle(TreeNodesRenderingNotification notification)
    {
        // this example will filter any content tree node whose node name starts with
        // 'Private', for any user that is in the customUserGroup
        if (notification.TreeAlias.Equals("content") &&
            _backOfficeSecurityAccessor.BackOfficeSecurity.CurrentUser.Groups.Any(f =>
                f.Alias.Equals("customUserGroupAlias")))
        {
            notification.Nodes.RemoveAll(node => node.Name.StartsWith("Private"));
        }
    }
}

MenuRenderingNotification

The MenuRenderingNotification is raised whenever a menu is generated for a tree node.

Members:

• MenuItemCollection Menu

• string NodeId

• FormCollection QueryString

• string TreeAlias

Usage:

using Umbraco.Cms.Core.Events;
using Umbraco.Cms.Core.Notifications;
using Umbraco.Cms.Core.Security;

public class TreeNotificationHandler : INotificationHandler<MenuRenderingNotification>
{
    private readonly IBackOfficeSecurityAccessor _backOfficeSecurityAccessor;

    public TreeNotificationHandler(IBackOfficeSecurityAccessor backOfficeSecurityAccessor)
    {
        _backOfficeSecurityAccessor = backOfficeSecurityAccessor;
    }

    public void Handle(MenuRenderingNotification notification)
    {
        // this example will add a custom menu item for all admin users

        // for all content tree nodes
        if (notification.TreeAlias.Equals("content") &&
            _backOfficeSecurityAccessor.BackOfficeSecurity.CurrentUser.Groups.Any(x =>
                x.Alias.InvariantEquals("admin")))
        {
            // Creates a menu action that will open /umbraco/currentSection/itemAlias.html
            var menuItem = new Umbraco.Cms.Core.Models.Trees.MenuItem("itemAlias", "Item name");

            // optional, if you don't want to follow the naming conventions, but do want to use a angular view
            // you can also use a direct path "../App_Plugins/my/long/url/to/view.html"
            menuItem.AdditionalData.Add("actionView", "my/long/url/to/view.html");

            // sets the icon to icon-wine-glass
            menuItem.Icon = "wine-glass";
            // insert at index 5
            notification.Menu.Items.Insert(5, menuItem);
        }
    }
}

Tree Actions and User Permissions

See a list of Tree Actions and User Permission Codes

When you type a search term into the Umbraco backoffice search field, you'll see search results from all the Section Trees that your user account has permission to access:

The results are grouped by 'Section Tree' like Content, Media, Document Types. Each 'Tree' has its own associated search mechanism that receives the search term and looks for matches in the tree that is responsible for searching.

You can create your own search mechanisms for your own custom sections or replace the default search implementation for a particular section tree.

Custom Tree Search

To create a search for your own custom tree you need to create a C# class that implements the interface Umbraco.Cms.Core.Trees.ISearchableTree.

ISearchableTree

using System.Collections.Generic;
using Umbraco.Cms.Core.Composing;
using Umbraco.Cms.Core.Models.ContentEditing;

namespace My.Website
{
    public interface ISearchableTree : IDiscoverable
    {
        /// <summary>
        /// The alias of the tree that the <see cref="ISearchableTree"/> belongs to
        /// </summary>
        string TreeAlias { get; }

        /// <summary>
        /// Searches for results based on the entity type
        /// </summary>
        /// <param name="query">The search term used for finding matching results.</param>
        /// <param name="pageSize">The number of records to return for a page of results.</param>
        /// <param name="pageIndex">The 0-based index for retrieving a page of search results.</param>
        /// <param name="totalFound">Populated with the total number of results matching the provided search term.</param>
        /// <param name="searchFrom">
        ///     The starting point for the search, generally a node ID, but for members this is a member type alias.
        /// </param>
        /// <returns></returns>
        Task<EntitySearchResults> SearchAsync(string query, int pageSize, long pageIndex, string? searchFrom = null);
    }
}

using System.Collections.Generic;
using Umbraco.Cms.Core.Composing;
using Umbraco.Cms.Core.Models.ContentEditing;

namespace My.Website
{
    public interface ISearchableTree : IDiscoverable
    {
        /// <summary>
        /// The alias of the tree that the <see cref="ISearchableTree"/> belongs to
        /// </summary>
        string TreeAlias { get; }

        /// <summary>
        /// Searches for results based on the entity type
        /// </summary>
        /// <param name="query">The search term used for finding matching results.</param>
        /// <param name="pageSize">The number of records to return for a page of results.</param>
        /// <param name="pageIndex">The 0-based index for retrieving a page of search results.</param>
        /// <param name="totalFound">Populated with the total number of results matching the provided search term.</param>
        /// <param name="searchFrom">
        ///     The starting point for the search, generally a node ID, but for members this is a member type alias.
        /// </param>
        /// <returns></returns>
        IEnumerable<SearchResultEntity> Search(string query, int pageSize, long pageIndex, out long totalFound, string searchFrom = null);
    }
}

Your implementation needs to return an IEnumerable of SearchResultEntity items:

public class SearchResultEntity : EntityBasic
{
    public SearchResultEntity() {
        /// <summary>
        /// The score of the search result
        /// </summary>
        [DataMember(Name = "score")]
        public float Score { get; set; }
    };

}

public class SearchResultEntity : EntityBasic
{
    public SearchResultEntity();

    /// <summary>
    /// The score of the search result
    /// </summary>
    [DataMember(Name = "score")]
    public float Score { get; set; }
}

A SearchResultEntity consists of a Score (a Float value) identifying its relevance to the search term, and the set of EntityBasic properties that all Umbraco objects share: eg Name, Id, Udi, Icon, Trashed, Key, ParentId, Path, Alias, AdditionalData.

Example implementation of ISearchableTree

If we have a custom section Tree with the alias 'favouriteThingsAlias' (see the custom tree example) then we could implement searchability by creating the following C# class in our site:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Umbraco.Cms.Core;
using Umbraco.Cms.Core.Models.ContentEditing;
using Umbraco.Cms.Core.Trees;

namespace Umbraco.Docs.Samples.Web.Trees
{
    public class FavouriteThingsSearchableTree : ISearchableTree
    {
        public string TreeAlias => "favouriteThingsAlias";

        public async Task<EntitySearchResults> SearchAsync(string query, int pageSize, long pageIndex, string searchFrom = null)
        {
            // your custom search implementation starts here
            Dictionary<int, string> favouriteThings = new Dictionary<int, string>();
            favouriteThings.Add(1, "Raindrops on Roses");
            favouriteThings.Add(2, "Whiskers on Kittens");
            favouriteThings.Add(3, "Skys full of Stars");
            favouriteThings.Add(4, "Warm Woolen Mittens");
            favouriteThings.Add(5, "Cream coloured Unicorns");
            favouriteThings.Add(6, "Schnitzel with Noodles");

            var searchResults = new List<SearchResultEntity>();

            var matchingItems = favouriteThings.Where(f => f.Value.StartsWith(query, true, System.Globalization.CultureInfo.CurrentCulture));
            foreach (var matchingItem in matchingItems)
            {
                // Making up the Id/Udi for this example! - these would normally be different for each search result.
                searchResults.Add(new SearchResultEntity()
                {
                    Id = 12345,
                    Alias = "favouriteThingItem",
                    Icon = "icon-favorite",
                    Key = new Guid("325746a0-ec1e-44e8-8f7b-6e7c4aab36d1"),
                    Name = matchingItem.Value,
                    ParentId = -1,
                    Path = "-1,12345",
                    Score = 1.0F,
                    Trashed = false,
                    Udi = Udi.Create("document", new Guid("325746a0-ec1e-44e8-8f7b-6e7c4aab36d1"))
                });
            }
            // Set number of search results found
            var totalFound = matchingItems.Count();
            // Return your results
            return new EntitySearchResults(searchResults, totalFound);
        }
    }
}

using System;
using System.Collections.Generic;
using System.Linq;
using Umbraco.Cms.Core;
using Umbraco.Cms.Core.Models.ContentEditing;
using Umbraco.Cms.Core.Trees;

namespace Umbraco.Docs.Samples.Web.Trees
{
    public class FavouriteThingsSearchableTree : ISearchableTree
    {
        public string TreeAlias => "favouriteThingsAlias";

        public IEnumerable<SearchResultEntity> Search(string query, int pageSize, long pageIndex, out long totalFound, string searchFrom = null)
        {
            // your custom search implementation starts here
            Dictionary<int, string> favouriteThings = new Dictionary<int, string>();
            favouriteThings.Add(1, "Raindrops on Roses");
            favouriteThings.Add(2, "Whiskers on Kittens");
            favouriteThings.Add(3, "Skys full of Stars");
            favouriteThings.Add(4, "Warm Woolen Mittens");
            favouriteThings.Add(5, "Cream coloured Unicorns");
            favouriteThings.Add(6, "Schnitzel with Noodles");

            var searchResults = new List<SearchResultEntity>();

            var matchingItems = favouriteThings.Where(f => f.Value.StartsWith(query, true, System.Globalization.CultureInfo.CurrentCulture));
            foreach (var matchingItem in matchingItems)
            {
                // Making up the Id/Udi for this example! - these would normally be different for each search result.
                searchResults.Add(new SearchResultEntity() { 
                    Id = 12345, 
                    Alias = "favouriteThingItem", 
                    Icon = "icon-favorite", 
                    Key = new Guid("325746a0-ec1e-44e8-8f7b-6e7c4aab36d1"), 
                    Name = matchingItem.Value, 
                    ParentId = -1, 
                    Path = "-1,12345", 
                    Score = 1.0F, 
                    Trashed = false, 
                    Udi = Udi.Create("document", new Guid("325746a0-ec1e-44e8-8f7b-6e7c4aab36d1")) 
                });
            }
            // Set number of search results found
            totalFound = matchingItems.Count();
            // Return your IEnumerable of SearchResultEntity
            return searchResults;
        }
    }
}

That's all we need, after an application pool recycle, if we now search in the backoffice we'll see matches from our custom 'Favourite Things' tree:

Umbraco automatically finds any implementation of ISearchableTree in your site and automatically configures it to be used for the custom section mentioned in the TreeAlias property. Be careful not to accidentally have two ISearchableTree implementations trying to search the 'same' TreeAlias, it's one ISearchableTree per TreeAlias.

Replacing an existing Section Tree Search

Perhaps you want to change the logic for searching an existing section of the site, (why? - well you might have a 'company name' property on a MemberType in the Member section, and you want searches for that company name to filter the members who work there, the default implementation will only search on Member Name).

Or perhaps you want to replace Examine search in the backoffice with an external Search Service, e.g. Azure Search. In a cloud-hosted implementation you don't need to build the Examine indexes on each new server as your cloud hosting scales out.

Example

First create your replacement custom ISearchableTree implementation, using the same approach as above, but specifying the TreeAlias of the Tree you aim to replace, e.g. 'Member'.

public string TreeAlias => "member";

To avoid your custom implementation clashing with the default ISearchableTree for a Tree, you need to remove its ISearchableTree implementation from the collection of SearchableTrees using an IComposer when Umbraco starts up:

using Umbraco.Cms.Core.Composing;
using Umbraco.Cms.Core.DependencyInjection;
using Umbraco.Cms.Web.BackOffice.Trees;

namespace Umbraco.Docs.Samples.Web.Trees
{
    public class RemoveCoreMemberSearchableTreeComposer : IComposer
    {
        public void Compose(IUmbracoBuilder builder)
        {
            // Remove core MemberTreeController
            builder.SearchableTrees().Exclude<MemberTreeController>();
        }
    }
}

This would then allow your custom implementation of ISearchableTree with TreeAlias 'member' to be used when searching the Member Section Tree.