wordpress add submenu

1add_menu_page('My Custom Page', 'My Custom Page', 'manage_options', 'my-top-level-slug');
2add_submenu_page( 'my-top-level-slug', 'My Custom Page', 'My Custom Page',
3    'manage_options', 'my-top-level-slug');
4add_submenu_page( 'my-top-level-slug', 'My Custom Submenu Page', 'My Custom Submenu Page',
5    'manage_options', 'my-secondary-slug');
6