DiagnosticsTreeController.cs

using System;
using System.Net.Http.Formatting;
using Umbraco.Core;
using Umbraco.Web.Models.Trees;
using Umbraco.Web.Mvc;
using Umbraco.Web.Trees;

namespace UmbracoDiagnostics
{
    [Tree("developer", "diagnosticsTree", "Diagnostics")]
    [PluginController("Diagnostics")]
    public class DiagnosticsTreeController : TreeController
    {
        protected override TreeNodeCollection GetTreeNodes(string id, FormDataCollection queryStrings)
        {
            //check if we're rendering the root node's children
            if (id == Constants.System.Root.ToInvariantString())
            {
                //Nodes that we will return
                var nodes   = new TreeNodeCollection();

                //Temp items for testing
                var items = new[] { "General", "Packages", "Users" , "Domains", "Assemblies", "Permissions", "Events", "MVC Routes", "Trees" };

                foreach (var item in items)
                {
                    //When clicked - /App_Plugins/Diagnostics/backoffice/diagnosticsTree/edit.html
                    //URL in address bar - /developer/diagnosticsTree/edit/General
                    var route       = string.Format("developer/diagnosticsTree/{0}", item);
                    var nodeToAdd   = CreateTreeNode(item, null, queryStrings, item, "icon-server", false, route);

                    //Add it to the collection
                    nodes.Add(nodeToAdd);
                }

                //Return the nodes
                return nodes;
            }

            //this tree doesn't suport rendering more than 1 level
            throw new NotSupportedException();
        }

        protected override MenuItemCollection GetMenuForNode(string id, FormDataCollection queryStrings)
        {
           throw new System.NotImplementedException();
        }
    }
}

var nodeToAdd = CreateTreeNode(item, null, queryStrings, item, "icon-server", false);

nodeToAdd.RoutePath = "/developer/diagnosticsTree/general/" + item.Id;

Hope it helps it's required to pass a id to the routepath