Can you add a user control recursively to itself?

Imagine some kind of tree control, where every node is again a tree control.

Each node is populated with a DataList containing the child nodes.

I manage to add additional instances of the user control to the
item template in the ItemDataBound handler, like this:

   Sub DataList1_ItemDataBound(sender As Object, e As
DataListItemEventArgs)
       If(e.Item.ItemType=ListItemType.Item Or
e.Item.ItemType=ListItemType.AlternatingItem) Then
           Dim testControl1 As New TestControl()
           e.Item.Controls.Add(testControl1)
           testControl1.BindDataList1()
       End If
   End Sub

In order to have a class name, I use this Control directive:
<%@ Control Language="VB" ClassName="TestControl" %>

This works perfectly.

But my question is: can I add the user control to the ItemTemplate
declaratively instead of programmatically, like this:

   <asp:DataList id="DataList1" OnItemDataBound="DataList1_ItemDataBound"
runat="server">
       <ItemTemplate>
            <TestControl id="testControl1" runat="server" />
       </ItemTemplate>
   </asp:DataList>

This still gives me no error, but now I need to refer to the control for
binding.

I try to bind it like this:
   Sub DataList1_ItemDataBound(sender As Object, e As
DataListItemEventArgs)
       If(e.Item.ItemType=ListItemType.Item Or
e.Item.ItemType=ListItemType.AlternatingItem) Then
           Dim testControl1 As TestControl =
CType(e.Item.FindControl("testControl1"),TestControl)
           testControl1.BindDataList1()
       End If
   End Sub

I get the error: specified cast is not valid.

How can I get this cast to work?

Thanks for your help,

Jos