[{"all":[{"type":"A","id":"1"},{"type":"A","id":"1"},{"type":"B","id":"2"},{"type":"A","id":"3"}]},{"all":[{"type":"A","id":"5"},{"type":"A","id":"4"},{"type":"B","id":"1"},{"type":"A","id":"11"}]}]

db.collection.aggregate([{$project:{list:{$filter:{input:"$all",as:"member",cond:{$eq:["$$member.type","A"]}}}}},{$group:{_id:null,unique_type_A:{$addToSet:"$list.id"}}}])