Usercontrol collection in Page

Hi all,
     I'm developing a :Webcontrol which collects all  "controls" in the container page which implement a certain interface.
My trouble is that in the page controls collection I can't seek "Usercontrol" at all.
Any suggestion?
 
 using WControl = System.Web.UI.Control;
  void RecurseControl(TreeNode node, WControl control)
     {

            foreach (WControl wctrl in control.Controls)
            {
                TreeNode cnode = new TreeNode(wctrl.UniqueID);
                if (wctrl is IConfigurableControl) ...