[{"QUERIES":[{"_id":ObjectId("5e71fa3ab004192b349e4a07"),"QUERY":"1","USER_ID":ObjectId("5e6f1c5b8451307f782d0994"),"USER_NAME":"a2","createdAt":ISODate("2020-03-18T10:38:50.247Z")},{"_id":ObjectId("5e71fa46b004192b349e4a08"),"QUERY":"2","USER_ID":ObjectId("5e6f1c5b8451307f782d0994"),"USER_NAME":"a1","createdAt":ISODate("2020-03-18T10:39:02.451Z")}],"TICKET_ID":ObjectId("5e70f4fa47df9479502f7937")}]

db.collection.aggregate([{$unwind:"$QUERIES"},{$sort:{"QUERIES.createdAt":-1}},{$group:{_id:{_id:"$_id",TICKET_ID:"$TICKET_ID"},QUERIES:{$push:"$QUERIES"}}},{$replaceRoot:{newRoot:{$mergeObjects:["$$ROOT","$_id"]}}}])