<?php
$Pages = wp_list_pages('title_li=&echo=0&depth=1');
$InnerPages = wp_list_pages('child_of='.($post->post_parent != false ? $post->post_parent : $post->ID).'&title_li=&echo=0');
$Title = ($post->post_parent != false) ? trim(get_the_title($post->post_parent)) : trim(wp_title('', false));
if($Title != '')
$Pages = str_replace($Title.'</a></li>',
$Title.'</a>'.
'<ul>'.$InnerPages.'</ul></li>',
$Pages);
echo $Pages;
unset($Pages, $InnerPages);
?>
It’s a slightly dirty method but it works…