[{"status":"Complete","level":"High"},{"status":"Incomplete","level":"Low"},{"status":"Complete","level":"Medium"}]

db.collection.aggregate([{"$set":{"sort-key":{"$switch":{"branches":[{"case":{"$eq":["$level","High"]},"then":0},{"case":{"$eq":["$level","Medium"]},"then":1}],"default":2}}}},{"$sort":{"sort-key":1}},{"$unset":["sort-key"]}])