[{_id:ObjectId("6384557894421b5e9d7aa7ea"),region:"US",name:"United State",},{_id:ObjectId("6384557894421b5e9d7aa7eb"),region:"US",name:"United State",}]

db.collection.aggregate([{$group:{"id":{"$push":"$_id"},_id:{region:"$region",name:"$name"},priority:{$sum:1}}},{$project:{code:"$_id.region",name:"$_id.name",priority:"$priority",id:1}}])