i was about to forget to refer to the updateprogress control in the
atlas framework i think u gonna like this so let me add this 2 lines of
code.
<atlas:ScriptManager ID="sm1" runat="server"
EnablePartialRendering="true"></atlas:ScriptManager>
<atlas:UpdatePanel ID="up1" runat="server">
<ContentTemplate>
<atlas:UpdateProgress ID="process1" runat="server">
<ProgressTemplate>
<div class="title" style="font-weight: bold;
vertical-align: middle; text-transform: capitalize;
color: #cc6600; font-family: 'Arial Narrow', 'Arial
Black'; letter-spacing: 10px;
text-align: center">
<img alt="" src="../loading.gif" style="width: 55px;
height: 55px" /><br />
<br />
Loading</div>
</ProgressTemplate>
</atlas:UpdateProgress>
</ContentTemplate>
</atlas:UpdatePanel>
ofcourse u gonna need a cool loading.gif just goo google images search
for loading.gif u will find some cool stuff pick one and after adding
the updateprogress control with your treeview control inside the update
panel u will have dymanic client-side tree control with some cool
loading styles

i love atlas
Sharing makes All the Difference