Add Drag and Drop in ul, li multilevel costume tree view using JQuery without any Plugin

I have created custom tree view using ui and li.
I want to add drag and drop on top of it without any custom plugin. Any child can be dragged in inside any li node.

like in this image 3rd parties can drag into Asset Management as child.
enter image description here

I have used $("$id").sortable(); but it’s just working in single child level only, i want to add it on multilevel.

example : http://wwwendt.de/tech/fancytree/demo/sample-ext-dnd.html