How to Identifying the asp treeview node value path?

Question

Hai,

In my app i have two asp treeview controls named Treeview1, Treeview2, and four buttons named
ADD, REMOVE,ADDALL, REMOVEALL.

In the first Treeview i selected a treenode and clicked ADD button then it will added to the second treeview successfullly. if i add again that node, again it will be added to Second treeview, How i can prevent this,
I wrote the following one

TreeNode node = TreeView2.FindNode(TreeView1.SelectedNode.ValuePath);

if (node != null)
       
   {
   Response.wripte("This node is already exists");
        return;
}
   but not identify for all cases,
if u know help me