protected void TreeView1_TreeNodeExpanded(object sender, TreeNodeEventArgs e)

         {

              TreeNodeCollection ts = null;

             if (e.Node.Parent == null)

             {

                 ts = ((TreeView)sender).Nodes;

             }

             else

                 ts = e.Node.Parent.ChildNodes;

             foreach (TreeNode node in ts)

             {

                 if (node != e.Node)

                 {

                     node.Collapse();

                 }

             }

         }