[{orientation:"portrait",size:"45",columns:2,type:1,_id:"c5ea1968-6ab5-4b05-80a9-db9dabe29dde"},{orientation:"landscape",size:"45",columns:3,type:1,_id:"37186b8e-4033-46c6-8b2e-82ee45f96904"},{orientation:"portrait",size:"45",columns:2,type:1,_id:"8f49a3ff-2859-4027-b644-88ac0949808d"},{orientation:"portrait",size:"45",columns:2,type:2,_id:"862717f4-2ef7-4839-947a-02771338c38c"},{orientation:"portrait",size:"45",columns:2,type:3,_id:"e1a93b10-dfcb-42a2-955a-ee14d539624f"}]

db.collection.aggregate([{"$group":{"_id":{"orientation":"$orientation","columns":"$columns","type":"$type"},"list":{"$first":"$$ROOT"}}},{"$group":{"_id":"$_id.type","list":{"$push":"$list"}}}])