Thanks a lot

The same code in C#:

   protected void RadTreeView1_NodeCreated(object sender, Telerik.Web.UI.RadTreeNodeEventArgs e)
   {
       e.Node.Expanded = true;
   }

Markup:

<telerik:RadTreeView ID ="trv" ... OnNodeCreated="RadTreeView1_NodeCreated">
</telerik:RadTreeView>