问如何只添加顶级管理菜单而不创建子级菜单

EN

add_action( 'admin_menu', 'travel_site' );

function travel_site(){
    add_menu_page( 'Travel Site Menu', 'Travel Site', 'manage_options', 'travel-site-menu', 'ts_admin_main_page' );
    add_submenu_page("travel-site-menu","View Travel Requests","View Travel Requests","manage_options","ts-view-travel-requests","ts_admin_vtr_page");
}

function ts_admin_main_page(){
    echo '<div class="wrap">';
    echo    '<p>Testing main travel site menu page</p>';
    echo '</div>';
}

function ts_admin_vtr_page(){
    echo '<div class="wrap">';
    echo    '<p>Testing view travel requests</p>';
    echo '</div>';
}