See Also: MenuItem Members
The Gtk.MenuItem and derived widgets are the only valid children for menus. Their function is to correctly handle highlighting, alignment, events and submenus.
C# Example
MenuBar mb = new MenuBar ();
Menu file_menu = new Menu ();
MenuItem exit_item = new MenuItem("Exit");
file_menu.Append (exit_item);
MenuItem file_item = new MenuItem("File");
file_item.Submenu = file_menu;
mb.Append (file_item);