Customisation of wp_list_pages

I would like to generate a list of pages on my site in the following format

[please use backticks or the code button to mark your code]

<ul class="menu">

<li><h3>Top level item</h3>
<ul>
<li>Second level item</li>
<li>Second level item</li>
</ul>
</li>

As you can see it is not only a question of adding a depth of 2, the problem lies in the fact that I want an H3 only for top level items, how can I do this? Thanks.