title: Prevent drag drop on child nodes of DotNetBar AdvTree/TreeControl
body: <p>I'm implementing a TreeControl using the DotNetBar Advtree component.  However I seem to be struggling to find the property to make it impossible for a particular node to have any children.  What I want to stop the following below;</p>
  
  <p><img src="https://i.stack.imgur.com/jDtRn.png" alt="How to stop this with the TreeControl component?"></p>
  
  <p>For example an RSS feed cannot be contained with an RSS feed.  Some in effect I want some nodes to be draggable, and can have children, and others only draggable.</p>
  
  <p><img src="https://i.stack.imgur.com/8xibX.png" alt="enter image description here"></p>
  
  <p>Thanks for any help.  I've noticed the property NodesIndent which I've setting to -1, or 5000 but neither was any help.</p>