title: get the expanding node in a treeview
body: <p>I have a treeview control that functions like a folder browser.
  Because loading the entire folder structer from disk is taking a lot of time i'm trying to load only one level at a time.
  So i have a function that adds nodes for all the folders in the current node.</p>
  
  <p>I thought that the best method would be to run it on the <code>BeforeExpand</code> event of the treeview.</p>
  
  <pre><code>UpdateTreeView(TreeView.SelectedNode);
  </code></pre>
  
  <p>is not working because clicking the + sign to expand is not selecting the node also.</p>
  
  <p>So how  to find the node that is expanding.</p>