help with sortable list

help with sortable list


How after sort action i can get new LI position ?
need send new position to php engine and change position in db
tree....
<ul class="listtree">
<li>1</li>
<li>2
<ul>
<li>2.1</li>
</ul>
</li>
<li>3</li>
</ul>
<script>
    $(".listtree").sortable({
        items: "LI",
        stop: function(e, ui) {update_sorting(e, ui)}
        });
function update_sorting(e, ui)
{
// ????????????????
}
</script>