How to achieve nested lists with rubaxa sortable.js

I'm using Rubaxas Sortable.js to be able to sort lists.My problem is that i can only move the ".group_container" to the bottom of the main holder but not inbetween the other lists.Heres a jsFiddle https://jsfiddle.net/adishardis/6csou39n/4/ <h1>Sortable</h1><div class="group" id="main"> <div class="group group_container" id="group1"> a <div class="question">item 1</div> <div class="question">item 2</div> <div class="question">item 3</div> </div> <div class="gro...Read more