<?php
	$pages = get_pages( array(
		    	'sort_column' => 'menu_order',
		    	'parent' => 0)
				);
	?>

	<?php
		if ($post->post_parent)
			//I am a subpage
			$id = $post->post_parent;
		else
			//I am a page
			$id = $post->ID;

		$subpages = get_pages(array("child_of"=>$id));
	?>

<?php foreach ($pages as $page):?>
	<li>

		<a href="<?php echo get_permalink($page->ID); ?> "><?php echo $page->post_title ?></a>
		<?php
		if ( ($page->ID == $post->ID) || ($post->post_parent == $page->ID) ):

		?>
		<ul>
			<?php
				foreach($subpages as $subpage):
			?>
			<li>
				<a href="<?php echo get_permalink($subpage->ID); ?> "><?php echo $subpage->post_title ?></a>
			</li>
			<?php endforeach; ?>
		</ul>
		<?php endif; ?>
	</li>

<?php endforeach;?>