Database
db={"Cities":[{"_id":1,"Name":"Santa Monica","State":"California"},{"_id":{"$oid":"5ec5fcc993ce00388429278a"},"Name":"Santa Monica","State":"California","TimeZone":"UTC−8","Population":90401}]}
Query
db.Cities.aggregate([{$group:{_id:{"Name":"$Name","State":"$State"},data:{$push:"$$ROOT"}}},{"$replaceWith":{"$mergeObjects":{"$reverseArray":"$data"}}}])