Expand/open a context menu's sub menu item programmatically

public partial class RadForm1 : Telerik.WinControls.UI.RadForm
{
    private RadContextMenu contextMenu;
    public RadForm1()
    {
        InitializeComponent();
        contextMenu = new RadContextMenu();
        RadMenuItem menuItem1 = new RadMenuItem("Item 1");
        RadMenuItem menuItem2 = new RadMenuItem("Item 2");
        RadMenuItem menuItem3 = new RadMenuItem("Sub menu item 1");
        RadMenuItem menuItem4 = new RadMenuItem("Sub menu item 2");
        menuItem2.Items.Add(menuItem3);
        menuItem2.Items.Add(menuItem4);
        contextMenu.Items.Add(menuItem1);
        contextMenu.Items.Add(menuItem2);
        this.radGridView1.ContextMenuOpening += this.RadGridView1_ContextMenuOpening;
        contextMenu.DropDownOpened += this.ContextMenu_DropDownOpened;
    }

    private void ContextMenu_DropDownOpened(object sender, EventArgs e)
    {
        foreach (RadMenuItem item in contextMenu.Items)
        {
            if (item.HasChildItemsToShow)
            {
                item.ShowChildItems();
            }
        }
    }

    private void RadGridView1_ContextMenuOpening(object sender, ContextMenuOpeningEventArgs e)
    {
        e.ContextMenu = contextMenu.DropDown;
    }