Create your own renderer that uses a JPanel with two labels in it.

Nest the labels using a BorderLayout, something like

  JPanel p = new JPanel(new BorderLayout());
  JLabel iconOnly = new JLabel(someIcon);
  JLabel iconAndText = new JLabel(someText,anotherIcon);
  p.add(iconOnly, BorderLayout.WEST);
  p.add(iconAndText, BorderLayout.CENTER);

See the Swing FAQs for how to write renderers

Implement the javax.swing.Icon Interface in a class which delegates the painting to two other Icons (javax.swing.ImageIcons say !). It should also report the correct height (max height of the two delgates)and width (sum of the widths of two delegates). (This assumes you want to show two images side by side).
Now set an instance of this Icon implementation as the icon of the TreeCellRendeder JLabel using setIcon().

In fact you can generalize this to paint a series of images side-by-side or grid or whatever.