mongodb聚合管道子集排序如何实现

mongodb聚合管道排序使用$sort , mongodb聚合管道子集排序如何实现呢，参考下面代码：

{
    $group: {
        _id: {
            name: '$name',
            quantity: '$quantity',
            year: {$year: '$updatedAt'},
            month: {$month: '$updatedAt'},
            dayOfMonth: {$dayOfMonth: '$updatedAt'}
        },    
        totalAmountSold: { $sum :'$modified_quantity' },
    }
},
{
    $sort: {
        "_id.year": 1,
        "_id.month": 1,
        "_id.dayOfMonth": 1,
    }
}