[WP] Function: is_tree()

/**
 * is_tree()
 *
 * @url http://codex.wordpress.org/Conditional_Tags#Testing_for_sub-Pages
 */
if ( !function_exists ( 'is_tree' ) ) {

    function is_tree( $pid ) {      // $pid = The ID of the page we're looking for pages underneath

        // check only pages
        if (!is_page() )
            return false;

        // load details about this page
        global $post;

        // if a string is passed, get that page's id by path
        if ( is_string( $pid ) )
            $pid = get_page_by_path( $pid )->ID;

        // we're at the page or at a sub page
        if ( is_page( $pid ) )
            return true;

        // get all of the page's ancestors
        $anc = get_post_ancestors( $post->ID );
        // loop 'em
        foreach ( $anc as $ancestor ) {
            // untill finding the one that matches
            if( is_page() && $ancestor == $pid ) {
                return true;
            }
        }

        // we arn't at the page, and the page is not an ancestor
        return false;

    }

}

/**
 * Checks whether current page is a subpage or a top-level page
 *
 * @url http://codex.wordpress.org/Conditional_Tags#Testing_for_sub-Pages
 */
if ( !function_exists ( 'is_subpage' ) ) {

    function is_subpage() {

        // load details about this page
        global $post;

        // test to see if the page has a parent
        if ( is_page() && $post->post_parent ) {

            // the ID of the parent is this
            $parentID = $post->post_parent;
            // return the ID
            return $parentID;

        // there is no parent so...
        } else {
            // ...the answer to the question is false
            return false;
        }

    }

}