add_submenu_page( string $parent_slug, string $page_title, string $menu_title, string $capability, string $menu_slug, callable $function = '', int $position = null )

$parent_slug

自带的父级菜单别名有十几个

Dashboard(仪表盘): ‘index.php’

Posts(文章): ‘edit.php’

Media(媒体): ‘upload.php’

Pages(页面): ‘edit.php?post_type=page’

Comments(评论): ‘edit-comments.php’

Custom Post Types(自定义文章类型): ‘edit.php?post_type=your_post_type’

Appearance(外观): ‘themes.php’

Plugins(插件): ‘plugins.php’

Users(用户): ‘users.php’

Tools(工具): ‘tools.php’

Settings(设置): ‘options-general.php’

Network Settings: ‘settings.php’

add_submenu_page('index.php', 'page_title', 'menu_title', 'manage_options', 'menu_slug', array($this, 'add_submenu_page'), 1);
function add_submenu_page () {
	?>
	<h2>Submenu Page</h2>
	<?php
}