[{"tracked_item_type":"Software","tracked_item_name":"Word","duration":9540},{"tracked_item_type":"Software","tracked_item_name":"Excel","duration":4000},{"tracked_item_type":"Software","tracked_item_name":"Notepad","duration":4000},{"tracked_item_type":"Site","tracked_item_name":"Facebook","duration":7920},{"tracked_item_type":"Site","tracked_item_name":"Twitter","duration":5555},{"tracked_item_type":"Site","tracked_item_name":"Digital Blasphemy","duration":8000}]

db.collection.aggregate([{"$group":{"_id":{"tracked_item_type":"$tracked_item_type","tracked_item_name":"$tracked_item_name"},"duration":{"$sum":"$duration"}}},{"$sort":{"_id.tracked_item_type":1,"duration":-1}},{$group:{_id:"$_id.tracked_item_type",data:{$push:{tracked_item_name:"$_id.tracked_item_name",tracked_item_type:"$_id.tracked_item_type",duration:"$duration"}}}},{$project:{data:{$slice:["$data",2]},_id:0}},{$unwind:"$data"},{$replaceRoot:{newRoot:"$data"}}])