wordpress: is_tree function - Check if on certain page or on page children function

gistfile1.php

<?php 
function is_tree($pid) { 
    global $post;
    $anc = get_post_ancestors( $post->ID );
    foreach($anc as $ancestor) {
        if(is_page() && $ancestor == $pid) {
        return true;
    }
}
    if(is_page()&&(is_page($pid)))
        return true; 
    else
    return false;
};

/* Use like this */

if(is_tree(PAGE_ID)){
    // something
}