[{_id:1,Name:"ab",month:"JAN",achieved_score:"20%"},{_id:2,Name:"ab",month:"FEB",achieved_score:"40%"},{_id:3,Name:"ab",month:"MAR",achieved_score:"50%"},{_id:4,Name:"cd",month:"JAN",achieved_score:"50%"},{_id:5,Name:"cd",month:"FEB",achieved_score:"70%"},{_id:6,Name:"cd",month:"MAR",achieved_score:"60%"},{_id:7,Name:"ef",month:"FEB",achieved_score:"30%"},{_id:8,Name:"ef",month:"MAR",achieved_score:"40%"}]

db.collection.aggregate([{"$group":{"_id":"$Name","values":{"$addToSet":{"month":"$month","achieved_score":"$achieved_score"}}}}])