[{folder:"A",name:"Apple",color:"red"},{folder:"A",name:"Banana",color:"green"},{folder:"A",name:"Apple",color:"yellow"},{folder:"B",name:"Cherry",color:"green"}]

db.collection.aggregate([{$group:{_id:{folder:"$folder",name:"$name"},files:{$push:"$$ROOT"},},},{"$group":{"_id":"$_id.name","files":{$push:{"k":"$_id.name","v":"$files"}},"folder":{$first:"$files.folder"}}},{"$replaceRoot":{"newRoot":{"$mergeObjects":[{"$arrayToObject":"$files"},{"folder":{$first:"$folder"}}]}}},{"$group":{"_id":"$folder","data":{"$push":"$$ROOT"}}},{$group:{"_id":"$_id","d":{$push:{"k":"$_id","v":"$data"}}}},{"$replaceRoot":{"newRoot":{"$mergeObjects":[{"$arrayToObject":"$d"}]}}}])