title: TreeView: checkboxes only in child nodes
body: <p>I need a treeview control:</p>
  
  <ol>
  <li>Root nodes don't have checkboxes, only images.</li>
  <li>All child nodes have a checkbox + image.</li>
  </ol>
  
  <p>C#, .net 2.0, winforms (not wpf)</p>