public void HandleDrop(WinForms::IDataObject dragData)
   {
      if (!this.IsValidDropTarget(dragData))
         return;

      IEnumerable<TreeNode> draggedNodes = TreeView.GetTreeNodesFromDragData(dragData);
      if (draggedNodes == null)
         return;

      List<SelectionSetWrapper> selSets = new List<SelectionSetWrapper>();
      foreach (TreeNode tn in draggedNodes)
      {
         if (tn.Parent == null)
            continue;

         SelectionSetWrapper selSet = TreeMode.GetMaxNode(tn.Parent) as SelectionSetWrapper;
         if (selSet != null && !selSets.Contains(selSet))
            selSets.Add(selSet);
      }

      IEnumerable<IMaxNode> draggedMaxNodes = TreeMode.GetMaxNodes(draggedNodes);
      foreach (SelectionSetWrapper selSet in selSets)
      {
         IEnumerable<IMaxNode> newNodes = selSet.ChildNodes.Except(draggedMaxNodes);
         ModifySelectionSetCommand cmd = new ModifySelectionSetCommand(selSet, newNodes);
         cmd.Execute();
      }
   }
   public override void HandleDrop(WinForms::IDataObject dragData)
   {
      if (!this.IsValidDropTarget(dragData))
         return;

      IEnumerable<TreeNode> draggedNodes = TreeView.GetTreeNodesFromDragData(dragData);
      if (draggedNodes == null)
         return;

      IEnumerable<IMaxNode> draggedMaxNodes = TreeMode.GetMaxNodes(draggedNodes);
      SelectionSetWrapper targetSelSet = (SelectionSetWrapper)this.MaxNode;

      IEnumerable<IMaxNode> combinedNodes = targetSelSet.ChildNodes.Union(draggedMaxNodes);
      ModifySelectionSetCommand cmd = new ModifySelectionSetCommand(targetSelSet, combinedNodes);
      cmd.Execute();

      if (!ControlHelpers.ShiftPressed)
      {
         IEnumerable<SelectionSetWrapper> selSets = draggedNodes.Select(tn => TreeMode.GetMaxNode(tn.Parent))
                                                                .OfType<SelectionSetWrapper>()
                                                                .Where(n => !n.Equals(targetSelSet))
                                                                .Distinct();
         foreach (SelectionSetWrapper selSet in selSets)
         {
            IEnumerable<IMaxNode> newNodes = selSet.ChildNodes.Except(draggedMaxNodes);
            ModifySelectionSetCommand moveCmd = new ModifySelectionSetCommand(selSet, newNodes);
            moveCmd.Execute();
         }
      }
   }