[{_id:"MongoDB",parent:"Databases"},{_id:"dbm",parent:"Databases"},{_id:"Databases",parent:"Programming"},{_id:"Languages",parent:"Programming"},{_id:"Programming",parent:"Books"},{_id:"Programmings",parent:"meow"},{_id:"Books",parent:null}]

db.collection.aggregate({$match:{_id:"Books"}},{"$graphLookup":{"from":"collection","startWith":"$_id","connectFromField":"_id","connectToField":"parent","as":"ids"}},{$project:{"ids":{$map:{input:"$ids",as:"id",in:"$$id._id"}},"_id":0}})