function walk_page_dropdown_tree() {
	$args = func_get_args();
	if ( empty( $args[2]['walker'] ) ) { // the user's options are the third parameter
		$walker = new Walker_PageDropdown;
	} else {
		$walker = $args[2]['walker'];
	}

	return call_user_func_array( array( $walker, 'walk' ), $args );
}