[{id:1,parent_id:3,data:"bla bla"},{id:2,parent_id:null,data:"bla bla bla"},{id:3,parent_id:null,data:"bla"}]

db.collection.aggregate([{$match:{id:{$in:[1]}}},{$lookup:{from:"collection",localField:"parent_id",foreignField:"id",as:"parent"}},{$project:{all:{$concatArrays:["$parent",["$$ROOT"]]}}},{$project:{"all.parent":0}},{$unwind:"$all"},{$replaceRoot:{newRoot:"$all"}}])