Compute a tree from an array of objects with IDs and parent IDs
$ npm install unsplay>> var unsplay = require('unsplay');
>> unsplay([{id: 0}, {id: 1, pid: 0}], 'id', 'pid');
[{
item: {id: 0},
children: [{
item: {id: 1, pid: 0},
children: []
}]
}]