[{_id:ObjectId("63a9678da72f51f8dc89dfcf"),Country:"Afghanistan",Region:"ASIA (EX. NEAR EAST)",Population:31056997,"Area (sq":{" mi":{")":647500}},"Net migration":"23,06",Climate:0,Birthrate:46.6,Deathrate:20.34,Agriculture:0.38,},{_id:1,Country:"A",Region:"ASIA (EX. NEAR EAST)",Birthrate:1},{_id:2,Country:"B",Region:"ASIA (EX. NEAR EAST)",Birthrate:2},{_id:3,Country:"C",Region:"EUROPE",Birthrate:1,},{_id:4,Country:"D",Region:"EUROPE",Birthrate:0.5}]

db.collection.aggregate([{"$match":{"Birthrate":{"$lt":20}}},{"$sort":{"Birthrate":1}},{"$group":{"_id":"$Region","country":{"$first":"$$ROOT"}}}])