[{"_id":ObjectId("62f45101c6b6654eafcf8859"),"parentId":null,"status":1},{"_id":ObjectId("62f45e6c74f4f1d1cf4bc73a"),"parentId":ObjectId("62f45101c6b6654eafcf8859"),"status":4},{"_id":ObjectId("62f45e6c74f4f1d1cf4bc73b"),"parentId":ObjectId("62f45101c6b6654eafcf8859"),"status":3}]

db.collection.aggregate([{$lookup:{from:"collection",localField:"_id",foreignField:"parentId",as:"children"}},{"$project":{status:{"$cond":{"if":{"$eq":["$parentId",null]},"then":{"$min":"$children.status"},"else":"$status"}},parentId:1}},{"$merge":{"into":"collection","on":"_id","whenMatched":"replace",}}])