Java JTree remove icon

import java.awt.Color;
import java.awt.Component;
import java.awt.Graphics;

import javax.swing.Icon;
import javax.swing.JFrame;
import javax.swing.JScrollPane;
import javax.swing.JTree;
import javax.swing.tree.DefaultMutableTreeNode;
import javax.swing.tree.DefaultTreeCellRenderer;
import javax.swing.tree.TreeSelectionModel;

public class Main {
   public static void main(String[] args) {
      DefaultMutableTreeNode rootNode = new DefaultMutableTreeNode("Root");
      DefaultMutableTreeNode a = new DefaultMutableTreeNode("A");
      rootNode.add(a);/*from w  w  w .ja  v a  2  s  . c o m*/

      DefaultMutableTreeNode a1 = new DefaultMutableTreeNode("1");
      a.add(a1);
      DefaultMutableTreeNode a2 = new DefaultMutableTreeNode("2");
      a.add(a2);

      DefaultMutableTreeNode b = new DefaultMutableTreeNode("B");
      rootNode.add(b);
      DefaultMutableTreeNode b1 = new DefaultMutableTreeNode("1");
      b.add(b1);

      JTree tree = new JTree(rootNode);

      DefaultTreeCellRenderer renderer = (DefaultTreeCellRenderer) tree.getCellRenderer();
      renderer.setOpenIcon(new SquareIcon());
      
      renderer.setLeafIcon(null);
      renderer.setClosedIcon(null);
      renderer.setOpenIcon(null);
      
      tree.getSelectionModel().setSelectionMode(TreeSelectionModel.SINGLE_TREE_SELECTION);

      JFrame f = new JFrame();
      f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      f.add(new JScrollPane(tree));
      f.setSize(250, 250);
      f.setVisible(true);
   }

}
class SquareIcon implements Icon {
   private static final int SIZE = 10;

   public void paintIcon(Component c, Graphics g, int x, int y) {
     if (c.isEnabled()) {
       g.setColor(Color.RED);
     } else {
       g.setColor(Color.GRAY);
     }

     g.fillRect(x, y, SIZE, SIZE);
   }

   public int getIconWidth() {
     return SIZE;
   }

   public int getIconHeight() {
     return SIZE;
   }
 }