Here, We can take multiple xml file as contextmenu..

 foreach (RadTreeNode node in RadTreeView1.GetAllNodes())
        {         
            if (node.Level == 0)
            {
                RadTreeViewContextMenu cn = new RadTreeViewContextMenu();
                cn.LoadContentFile("ContextMenu.xml");
                node.TreeView.ContextMenus.Add(cn);
                node.ContextMenuID = cn.ID;
            }
            else if (node.Level == 1)
            {
                RadTreeViewContextMenu cn = new RadTreeViewContextMenu();
                cn.LoadContentFile("ContextMenu1.xml");
                node.TreeView.ContextMenus.Add(cn);
                node.ContextMenuID = cn.ID;
            }
            else
            {
                RadTreeViewContextMenu cn = new RadTreeViewContextMenu();
                cn.LoadContentFile("ContextMenu2.xml");
                node.TreeView.ContextMenus.Add(cn);
                node.ContextMenuID = cn.ID;
            }

        }