[hardwired]

Code:

import java.awt.*;
import java.awt.event.*;
import java.util.Enumeration;
import javax.swing.*;
import javax.swing.tree.*;

public class NodeExpansion implements ActionListener {
    JTree tree = new JTree();

    public void actionPerformed(ActionEvent e) {
        String s = e.getActionCommand();
        setExpandedState(s);
    }

    private void setExpandedState(String id) {
        DefaultMutableTreeNode root =
            (DefaultMutableTreeNode)tree.getModel().getRoot();
        Enumeration e = root.breadthFirstEnumeration();
        while(e.hasMoreElements()) {
            DefaultMutableTreeNode node = (DefaultMutableTreeNode)e.nextElement();
            if(node.getUserObject().equals(id)) {
                TreePath path = new TreePath(node.getPath());
                if(node.isLeaf()) {
                    DefaultMutableTreeNode parent =
                        (DefaultMutableTreeNode)node.getParent();
                    expandNode(new TreePath(parent.getPath()));
                } else {
                    expandNode(path);
                }
                tree.setSelectionPath(path);
                break;
            }
        }
    }

    private void expandNode(TreePath parent) {
        TreeNode node = (TreeNode)parent.getLastPathComponent();
        if (node.getChildCount() >= 0) {
            Enumeration e = node.children();
            while(e.hasMoreElements()) {
                TreeNode n = (TreeNode)e.nextElement();
                TreePath path = parent.pathByAddingChild(n);
                expandNode(path);
            }
        }
        tree.expandPath(parent);
    }

    private JPanel getContent() {
        JPanel panel = new JPanel(new GridLayout(1,0));
        panel.add(new JScrollPane(tree));
        panel.add(getRightComponent());
        return panel;
    }

    private JScrollPane getRightComponent() {
        ButtonGroup group = new ButtonGroup();
        JPanel panel = new JPanel(new GridBagLayout());
        GridBagConstraints gbc = new GridBagConstraints();
        gbc.insets = new Insets(2,5,2,0);
        gbc.weightx = 1.0;
        gbc.anchor = GridBagConstraints.WEST;
        gbc.gridwidth = GridBagConstraints.REMAINDER;
        TreeModel model = tree.getModel();
        DefaultMutableTreeNode root = (DefaultMutableTreeNode)model.getRoot();
        Enumeration e = root.breadthFirstEnumeration();
        while(e.hasMoreElements()) {
            DefaultMutableTreeNode node = (DefaultMutableTreeNode)e.nextElement();
            String s = node.getUserObject().toString();
            JRadioButton rb = new JRadioButton(s);
            rb.setActionCommand(s);
            rb.addActionListener(this);
            group.add(rb);
            panel.add(rb, gbc);
        }
        return new JScrollPane(panel);
    }

    public static void main(String[] args) {
        JFrame f = new JFrame();
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.add(new NodeExpansion().getContent());
        f.setSize(500,400);
        f.setLocation(200,200);
        f.setVisible(true);
    }
}