[{year:"2000",language:"English",genre:"Romance",name:"A beautiful day"},{year:"2000",language:"English",genre:"Action",name:"A Dangerous day"},{year:"2000",language:"French",genre:"Romance",name:"someromancename"},{year:"2000",language:"French",genre:"Action",name:"someactionname"}]

db.collection.aggregate([{$group:{_id:{"year":"$year","language":"$language","genre":"$genre"},"movies":{"$push":{name:"$name"}}}},{$group:{_id:{year:"$_id.year",language:"$_id.language"},"movies":{"$push":{k:"$_id.genre",v:"$movies"}}}},{$group:{_id:"$_id.year",movies:{$push:{k:"$_id.language",v:{$arrayToObject:"$movies"}}}}},{$replaceRoot:{newRoot:{$arrayToObject:[[{k:"$_id",v:{$arrayToObject:"$movies"}}]]}}}])