Code to add all parent pages

WP_nav.php

<?php
    if(!$post->post_parent){
         $children = wp_list_pages("title_li=&child_of=".$post->ID."&echo=0&depth=1");
    }else{
	  if($post->ancestors){
		$ancestors = array_reverse($post->ancestors, true);
		foreach($ancestors as $ancestor){
			$ancestor = wp_list_pages("title_li=&child_of=".$ancestor."&echo=0&depth=1");
			echo "<ul>";
			echo $ancestor;
			echo "</ul>";
		}
		$children = wp_list_pages("title_li=&child_of=".$post->ID."&echo=0&depth=1");
	}
}
if ($children) { 
 	echo "<ul>";
 	echo $children; 
 	echo "</ul>";
}
?>