[{"_id":{"year_month":"2022-01","client_name":"client A","client_label":"client A","client_code":0,"client_country":"TH","base_curr":"USD","inv_curr":"USD","dest_curr":"HKD"},"total_vol":100000,"total_tran":100}]

db.collection.aggregate([{"$replaceWith":{"$mergeObjects":["$$ROOT","$_id"]}},{$unset:"_id"}])