Extend a new method called 'getLevel' for tree, just like this.
<script>
$.extend($.fn.tree.methods,{
getLevel: function(jq, target){
return $(target).find('span.tree-indent,span.tree-hit').length;
}
});
</script>
Now, rewrite your code as below:
var level = $('#test').combotree('tree').tree('getLevel', node.target);
alert(level);