c# TreeViewに右クリックイベントを登録する

-TreeView のアイテムを右クリックした場合にポップアップメニューを表示する。

using System;
using System.Windows.Forms;
using System.Drawing;

class FormMain : Form {

    private TreeView menuTreeView;
    private ContextMenuStrip docMenu;

    [STAThread]
    public static void Main() {
        Application.EnableVisualStyles();
        Application.SetCompatibleTextRenderingDefault(false);
        Application.Run( new FormMain());
    }

    FormMain()
    {
        InitializeMenuTreeView();
    }

    public void contextMenuStrip_SubMenuClick(object sender, EventArgs e)
    {
        string s = ((ToolStripMenuItem)sender).Text;

        MessageBox.Show("Item is " + s, "Item Clicke");
    }

    public void InitializeMenuTreeView()
    {
        // Create the TreeView.
        menuTreeView = new TreeView();
        menuTreeView.Size = new Size(200, 200);

        // Create the root node.
        TreeNode docNode = new TreeNode("Documents");

        // Add some additional nodes.
        docNode.Nodes.Add("phoneList.doc");
        docNode.Nodes.Add("resume.doc");

        // Add the root nodes to the TreeView.
        menuTreeView.Nodes.Add(docNode);

        // Create the ContextMenuStrip.
        docMenu = new ContextMenuStrip();

        //Create some menu items.
        ToolStripMenuItem openLabel = new ToolStripMenuItem();
        openLabel.Text = "Open";
        ToolStripMenuItem deleteLabel = new ToolStripMenuItem();
        deleteLabel.Text = "Delete";
        ToolStripMenuItem renameLabel = new ToolStripMenuItem();
        renameLabel.Text = "Rename";

        openLabel.Click += contextMenuStrip_SubMenuClick;
        deleteLabel.Click += contextMenuStrip_SubMenuClick;
        renameLabel.Click += contextMenuStrip_SubMenuClick;

        //Add the menu items to the menu.
        docMenu.Items.AddRange(new ToolStripMenuItem[]{openLabel, 
            deleteLabel, renameLabel});

        // Set the ContextMenuStrip property to the ContextMenuStrip.
        docNode.ContextMenuStrip = docMenu;

        // Add the TreeView to the form.
        this.Controls.Add(menuTreeView);
    }
}