docs: protected JScrollPane createScroller() {
      JScrollPane sp = new JScrollPane(tree, ScrollPaneConstants.VERTICAL_SCROLLBAR_AS_NEEDED, ScrollPaneConstants.HORIZONTAL_SCROLLBAR_NEVER);
      sp.setHorizontalScrollBar(null);
      sp.setName("TreePopup.scrollPane");
      sp.setFocusable(false);
      sp.getVerticalScrollBar().setFocusable(false);
      sp.setBorder(null);
      return sp;
    }