[{directComputers:[{_id:ObjectId("6139f794f6a0af371900dbfa"),name:"MyComputer_1"},{_id:ObjectId("6319bd1540b41d1a35717a16"),name:"MyComputer_2"}],indirectComputers:[{_id:ObjectId("6319bd1540b41d1a35717a16"),name:"MyComputer_2"},{_id:ObjectId("61f39f8ae2daa732deff6d90"),name:"MyComputer_3"}]}]

db.collection.aggregate([{$project:{_id:0,data:{$concatArrays:["$directComputers","$indirectComputers"]}}},{$unwind:"$data"},{$group:{_id:"$data._id",name:{$first:"$data.name"}}}])