I found the solution!

I've create a new User Type, in this example I called it "Custom User", then I check if the loggedin user is the Admin or is a Custom User.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using umbraco.cms.presentation.Trees;
using System.Web;
using umbraco.BusinessLogic;

namespace MyCustomTools
{
public class LoadCustomTools : BaseTree
{
public LoadCustomTools(string application)
: base(application)
{ }

protected override void CreateRootNode(ref XmlTreeNode rootNode)
{
rootNode.Icon = FolderIcon;
rootNode.OpenIcon = FolderIconOpen;
rootNode.NodeType = "init" + TreeAlias; rootNode.NodeID = "init";
}

/// Override the render method to create the custom tree
public override void Render(ref XmlTree Tree)
{
User user = User.GetCurrent();

if (user.IsAdmin() || user.UserType.Alias == "Custom User")
{
if (this.id == this.StartNodeID)
{
var Folder = XmlTreeNode.Create(this);
Folder.NodeID = "2";
Folder.Text = "Custom Folder";
Folder.Icon = FolderIcon;
Folder.OpenIcon = FolderIconOpen;
Folder.HasChildren = true;
Folder.Source = this.GetTreeServiceUrl(2);
Tree.Add(Folder);
} else if (this.id == 2) {
var customNode = XmlTreeNode.Create(this);
customNode.Text = "My Custom Node";
customNode.Icon = "docPic.gif";
customNode.Action = "javascript:openCustomNode()";
Tree.Add(customNode);
}
}
}

public override void RenderJS(ref StringBuilder Javascript) {
Javascript.Append(@"
function openCustomNode() {
parent.right.document.location.href = '/handlers/somehandler.aspx';
}
");
}
}
}