[{"id":1,"name":"John","designation":"customer"},{"id":2,"name":"Alison","designation":"manager"},{"id":3,"name":"Sam","designation":"customer"},{"id":4,"name":"George","designation":"salesperson"},{"id":5,"name":"Will","designation":"salesperson"},{"id":6,"name":"Daffney","designation":"customer"},{"id":7,"name":"Julie","designation":"salesperson"},{"id":8,"name":"Elliot","designation":"customer"},{"id":9,"name":"Bruno","designation":"customer"},{"id":10,"name":"Omar","designation":"customer"},{"id":11,"name":"Sid","designation":"customer"},{"id":12,"name":"Nelson","designation":"manager"}]

db.collection.aggregate([{"$bucketAuto":{groupBy:"$designation",buckets:5,output:{"count":{$sum:1},"users":{$push:{"name":"$name"}}}}},{$addFields:{users:{$slice:["$users",2]}}},{$addFields:{count:{$size:"$users"}}}])