RadTreeListView : ColumnView issue

Question

Hi, I am very much new to the Silverlight. We have an application using with Silverlight, WCF and Telerik controls.

I am using RadTreeListView. in RadTreeListView i have used custom columns as below

<radNavigation:RadTreeListView.Columns>
          <radNavigation:RadColumn CellTemplate="{StaticResource CustomNodeTemplate}"  IsSortable="False" PropertyName="Name" Width="Auto"/>
</radNavigation:RadTreeListView.Columns>

When i am running the application, above tree there is one small rectangle is coming. i am not sure what it is. When click on that small rectangle tree view hides from UI. Don't no what is happening over there. When i can see through spy, it is showing me as ColumnView. Not sure how to hide it or resize it.

Can anyone have idea, to solve the issue?

Thanks, Mahesh.