Custom Server Controls :: Using Inherited TreeView And TreeNode

I am trying to extend the TreeView and TreeNode class and use it in an .aspx page. My development environment is VS 2005. I put the following code inside of a single .cs file in my App_Code folder:

public class MyTreeview : TreeView {
protected override void TreeNode CreateNode() { return new MyTreeNode(); }
}
public class MyTreeNode: TreeNode { public MyTreeNode():base(){} }

I want to now use my inherited Node and TreeView in my .aspx file. I have the following directive, which is throwing an error -> File is in the special directory App_Code which is not allowed. I tried putting everything into an .ascx file, but I think I am not specifying the class and inheritance directives correctly.

<%
@
Register
TagPrefix="R7A"
TagName
="CoATree"
Src="../App_Code/ExtendedTreeNode.cs"........................