WP: Conditional to check for hierarchy descendant

gistfile1

// A conditional function to check if the current page is a descendant of the ID given to it. Useful for determining if a page is a grandchild, great-grandchild or father down the hierarchy tree.

function is_tree($pid) {      // $pid = The ID of the page we're looking for pages underneath
    global $post;         // load details about this page

    $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;   // we're at the page or at a sub page
    else 
               return false;  // we're elsewhere
}