[{"_id":ObjectId("5eaaeedd00101108e1123451"),"arrayfield":["admin","teacher","student"]},{"_id":ObjectId("5eaaeedd00101108e1123452"),"arrayfield":["admin","teacher","student"]},{"_id":ObjectId("5eaaeedd00101108e1123453"),"arrayfield":["student"],}]

db.collection.find({$expr:{$gt:[{$size:"$arrayfield"},1]}})