[{date:ISODate("2021-09-10T12:00:00+09:00"),Category:"usedCar",Data:[{name:"bmw",theNumberOfSold:15},{name:"Honda",theNumberOfSold:35},{name:"Toyota",theNumberOfSold:100}]},{date:ISODate("2021-09-11T12:00:00+09:00"),Category:"newCar",Data:[{name:"bmw",theNumberOfSold:5},{name:"Honda",theNumberOfSold:8},{name:"Toyota",theNumberOfSold:150}]}]

db.collection.aggregate([{$unwind:"$Data"},{$group:{_id:{year:{"$year":"$date"},month:{"$month":"$date"},name:"$Data.name"},totalAmount:{$sum:"$Data.theNumberOfSold"}}}])