我通过将主菜单slug放入自定义post类型数组的show\\u in\\u menu键来解决这个问题，如下所示：

$args = array (
        \'labels\' => $labels,
        \'hierarchical\' => FALSE,
        \'description\' => $title . \'s\',
        \'supports\' => array( \'title\' ),
        \'show_ui\' => TRUE,
        \'show_in_menu\' => \'squirrels_inventory\',
        \'show_in_nav_menus\' => TRUE,
        \'publicly_queryable\' => TRUE,
        \'exclude_from_search\' => FALSE,
        \'has_archive\' => TRUE
    );