@Override
    public boolean hasPreviousOccurence() {
      TreePath path = myTree.getSelectionPath();
      if (path == null) {
        return false;
      }
      DefaultMutableTreeNode node = (DefaultMutableTreeNode)path.getLastPathComponent();
      Object userObject = node.getUserObject();
      return userObject instanceof NodeDescriptor && !isFirst(node);
    }
@Override
    public boolean hasPreviousOccurence()