docs: public void show(Component parent) {
      Dimension parentSize = parent.getSize();
      Insets insets = getInsets();
  
      // reduce the width of the scrollpane by the insets so that the popup
      // is the same width as the combo box.
      parentSize.setSize(parentSize.width - (insets.right + insets.left), 10 * parentSize.height);
      Dimension scrollSize = computePopupBounds(parent, 0, getBounds().height, parentSize.width, parentSize.height).getSize();
  
      scroller.setMaximumSize(scrollSize);
      scroller.setPreferredSize(scrollSize);
      scroller.setMinimumSize(scrollSize);
  
      super.show(parent, 0, parent.getHeight());
      tree.requestFocusInWindow();
    }