I am currently working on an extension to Umbraco that needed an extra menu item on the Document Types menu in the Settings section, my first thought was to use the BeforeNodeRender event to add the menu item, but this event only fires on the Content and Media menu trees.

See: Codeplex Issue 21623

The "temporary" solution has been to extend the "loadNodeTypes" class, I say temporary because I assume that the core team may well extend the event functionality to the entire menu tree in the future which would be much better and would prevent you from having to complete override the menu items.

This was suggested by Slace on my "is it possible to add an item to the context menu in tree's other than media content" post on the our.umbraco.org site.

There are three things you need to do:

1) Override the loadNodeTypes

using System.Collections.Generic;
using umbraco.interfaces;
using umbraco.BusinessLogic.Actions;

namespace Vizioz.xMind2Umbraco
{
    // Note: Remember these menu's might change in future versions of Umbraco

    public class loadNodeTypesMenu : umbraco.loadNodeTypes
    {
        public loadNodeTypesMenu(string application) : base(application) { }

        protected override void CreateRootNodeActions(ref List<IAction> actions)
        {
            actions.Clear();
            actions.Add(ActionNew.Instance);
            actions.Add(xMindImportAction.Instance);
            actions.Add(ContextMenuSeperator.Instance);
            actions.Add(ActionImport.Instance);
            actions.Add(ContextMenuSeperator.Instance);
            actions.Add(ActionRefresh.Instance);
        }
        protected override void CreateAllowedActions(ref List<IAction> actions)
        {
            actions.Clear();
            actions.Add(ActionCopy.Instance);
            actions.Add(xMindImportAction.Instance);
            actions.Add(ContextMenuSeperator.Instance);
            actions.Add(ActionExport.Instance);
            actions.Add(ContextMenuSeperator.Instance);
            actions.Add(ActionDelete.Instance);
        }
    }
}

2) Create a new Action to be used on the menu

using umbraco.interfaces;

namespace Vizioz.xMind2Umbraco
{
    public class xMindImportAction : IAction
    {
        #region Implementation of IAction

        public static xMindImportAction Instance
        {
            get { return umbraco.Singleton<xMindImportAction>.Instance; }
        }

        public char Letter
        {
            get { return 'p'; }
        }

        public bool ShowInNotifier
        {
            get { return true; }
        }

        public bool CanBePermissionAssigned
        {
            get { return true; }
        }

        public string Icon
        {
            get { return "editor/OPEN.gif"; }
        }

        public string Alias
        {
            get { return "Import from xMind"; }
        }

        public string JsFunctionName
        {
            get
            {
                return "openModal('dialogs/xMindImport.aspx?id=' + nodeID, 
                                  'Publish Management', 550, 480);";
            }
        }

        public string JsSource
        {
            get { return string.Empty; }
        }

        #endregion
    }
}

3) Update the UmbracoAppTree table, my case I changed the following:

TreeHandlerType
From: loadNodeTypes
To: loadNodeTypesMenu

TreeHandlerAssembly
From: umbraco
To: Vizioz.xMind2Umbraco

And the result is: