Visual Studio .NET - Client-Side handling of treeview and listbox ctrl

You need to call the function by onselectedindexchange attribure.
U can get the node by  (Microsoft.Web.UI.WebControls.TreeViewSelectEventArgs e)  event
node_name =Treeview1.GetNodeFromIndex(e.NewNode).Text.ToString() ;

hope it will be useful fo r u.
Have a nice day
Surendra