您正在搜索的内容是一个子菜单页。尝试以下操作：

add_submenu_page( \'my-top-level-slug\', 
                  \'My Custom Submenu Page\', 
                  \'My Custom Submenu Page\',
                  \'manage_options\', 
                  \'my-secondary-slug\'
);

代码示例：

function my_plugins() {
    add_menu_page(
            \'My Plugin\', 
            \'My Plugin\', 
            \'manage_options\', 
            \'visitor-counter-by-funcion\', //THIS IS THE SLUG YOU NEED TO USE IN YOUR SUBMENU ITEMS
            \'my_custom_menu_page\', 
            \'dashicons-chart-bar\'
    );
    add_submenu_page(
            \'visitor-counter-by-funcion\', //THIS IS THE SLUG OF YOUR PARENT MENU PAGE
            \'My Custom Submenu Page\', 
            \'My Custom Submenu Page\', 
            \'manage_options\', 
            \'my-secondary-slug\', 
            \'my_custom_sub_menu_page\'
    );
}

add_action(\'admin_menu\', \'my_plugins\');

/**
 * Display a custom menu page
 */
function my_custom_menu_page() {
    esc_html_e(\'Admin Page Test\', \'textdomain\');
}

/**
 * Display callback for the submenu page.
 */
function my_custom_sub_menu_page() {
    ?>
    <div class="wrap">
        <h1><?php _e(\'My Custom Submenu Page\', \'textdomain\'); ?></h1>
        <p><?php _e(\'My Custom Submenu Page\', \'textdomain\'); ?></p>
    </div>
    <?php
}