<script type="text/javascript">
   var activenode = null;
   function $(id){return document.getElementById(id);}
   function AppySetting(){
      if (activenode!=null){
          activenode.setAttribute('AllowAdd'   ,(($('AllowAdd'   ).checked)? 'True':'False'));
          activenode.setAttribute('AllowEdit'  ,(($('AllowEdit'  ).checked)? 'True':'False'));
          activenode.setAttribute('AllowDelete',(($('AllowDelete').checked)? 'True':'False'));
      }
   }
   function OnClientNodeClicked(sender, args)
   {  
        activenode = args.get_node().get_attributes();
        $('AllowAdd'   ).checked = activenode.getAttribute('AllowAdd'   )=='True';
        $('AllowEdit'  ).checked = activenode.getAttribute('AllowEdit'  )=='True';
        $('AllowDelete').checked = activenode.getAttribute('AllowDelete')=='True';
   }
 </script>

server code :
aspx page
<telerik:RadTreeView id="RadTreeViewBackOffice" runat="server" CheckBoxes="True" TriStateCheckBoxes="true" CheckChildNodes="true" OnNodeDataBound="OnNodeDataBound"  OnClientNodeClicked="OnClientNodeClicked" OnClientNodeChecking="OnClientNodeClicked" />

code behind :

           e.Node.Attributes.Add("AllowDelete" ,"True");
} 

protected void OnClick(object sender, EventArgs e )

 {
  foreach(RadTreeNode Node in RadTreeViewBackOffice.CheckedNodes){
         Response.Write(Node.Attributes["AllowAdd"]);
  }