Database
[{name:"test1",score:80},{name:"test2",score:50},{name:"test3",score:100},{name:"test4",score:70}]
Query
db.collection.aggregate([{$addFields:{range:{$switch:{branches:[{case:{$lte:["$score",60]},then:"0-60"},{case:{$lte:["$score",90]},then:"61-90"},{case:{$lte:["$score",100]},then:"91-100"}],default:"invalid"}}}},{"$group":{"_id":"$range","tests":{"$push":"$name"}}}])