Sortable nested group improvement

[ShintaroNippon]

I'm using jQuery sortable on an element but when I drop down an element under other he set him as a child. Check please this behaviour to demonstrate: http://recordit.co/w8c5oXbnq4

I'm using sortable like this:

$('.sortable').sortable({ group: 'nested', handle: 'i.cat-move',

How can i set right behaviour without being a child? Thanks in advance