@Nullable
  @Override
  protected JComponent createCenterPanel() {
    ToolbarDecorator decorator = ToolbarDecorator.createDecorator(myTree).
      addExtraAction(new SelectAllButton()).
      addExtraAction(new UnselectAllButton()).
      setToolbarPosition(ActionToolbarPosition.BOTTOM);
    contentPanel.add(decorator.createPanel());
    return mainPanel;
  }
@Nullable
  @Override
  protected JComponent createCenterPanel()