Grouping collection by year and month in Laravel

I have a collection, that I would like to achieve group by the year and month.

2014
    jan
       2nd
       5th
       ...
    feb
       11th
       12th
       ...
    mar
    ...
2013
    jan
    feb
    mar
    ...
2012
    jan
    feb
    mar
    ...

this is my current collection but only by year. I couldn't get what I really wanted with this.

$collection =$model->orderBy('date', 'desc')->get()->groupBy(function($item) {
        return $item->date->format('Y');
    });

via Chebli Mohamed