您可以使用get_post_ancestors.根祖先是返回数组的最后一个元素。以下是根据当前页面的根祖先检查目标页面id的函数：

function check_page_parent( $target_page_id ) {
    $ancestors = get_post_ancestors( get_the_ID() );

    if ( $ancestors ) {
        $top_most_parent_index = count( $ancestors ) - 1;
        $top_most_parent_id    = $ancestors[ $top_most_parent_index ];

        return ( $top_most_parent_id == $target_page_id);
    }

    return false;
}