WordPress: is_tree

gistfile1

//Page List Navigation
function my_page_tree($this_page) {
	$pagelist = '';
	if( !$this_page->post_parent ) {
		$children = wp_list_pages('sort_column=menu_order&exclude=430&title_li=&child_of='.$this_page->ID.'&echo=0');
		if( $children ) {
			$pagelist .= '<li class="current_page_item"><a href="'.  get_page_link($this_page->ID) .'">' . $this_page->post_title . '</a>';
			$pagelist .= '<ul>' . $children . '</ul>';
			$pagelist .= '</li>';
		}
	}
	elseif( $this_page->ancestors ) {
		// get the top ID of this page. Page ids DESC so top level ID is the last one
		$ancestor = end($this_page->ancestors);
		$pagelist .= wp_list_pages('order=asc&sort_column=menu_order&exclude=430&title_li=&include='.$ancestor.'&echo=0');
		$pagelist = str_replace('</li>', '', $pagelist);
		$pagelist .= '<ul>' . wp_list_pages('order=asc&sort_column=menu_order&&exclude=430&title_li=&child_of='.$ancestor.'&echo=0') .'</ul></li>';

	}
	return $pagelist;
}

//Tree function
function is_tree($pid) {      // $pid = The ID of the page we're looking for pages underneath
	global $post;         // load details about this page
	if(is_page()&&($post->post_parent==$pid||is_page($pid)))
               return true;   // we're at the page or at a sub page
	else
               return false;  // we're elsewhere
};