Re-order child to a different parent

Hi all

I’ve gotten as far as being able to drag/reorder the children under their current parent, but I’d like the user to have the ability to drag the item to a different parent.

i.e. Drag “Holiday shopping” from Tuesday to Monday.

Can anyone point me in the right direction? So far… (I’ve reduce the JSON size to 2 days for readability):

Thanks in advance! Here’s the Code Pen:

http://codepen.io/anon/pen/wWwmjR