Add children DefaultMutableTreeNode to its parent in Java

 /*from w  ww  .j a  v a  2  s. c  om*/

import java.awt.BorderLayout;

import javax.swing.JFrame;
import javax.swing.JScrollPane;
import javax.swing.JTree;
import javax.swing.tree.DefaultMutableTreeNode;

public class Main {
  public static void main(String args[]) {
    JFrame frame = new JFrame();
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

    DefaultMutableTreeNode root = new DefaultMutableTreeNode("Root");
    DefaultMutableTreeNode mercury = new DefaultMutableTreeNode("Mercury");
    root.add(mercury);
    DefaultMutableTreeNode venus = new DefaultMutableTreeNode("Venus");
    root.add(venus);
    DefaultMutableTreeNode mars = new DefaultMutableTreeNode("Mars");
    root.add(mars);
    JTree tree = new JTree(root);

    JScrollPane scrollPane = new JScrollPane(tree);
    frame.add(scrollPane, BorderLayout.CENTER);
    frame.setSize(300, 150);
    frame.setVisible(true);
  }
}