[{"_id":"6032a5ad80443334a35f2232","List":[{"_id":"6032a5af80443334a35f2234","batch_id":"6032a5af80443334a5f74367UI","batchName":"Test 1",},{"_id":"6032a5b080443334a35f2236","batch_id":"6032a5af80443334a5f74367UI","batchName":"Test 1",},{"_id":"6032a5b080443334a35f2238","batch_id":"6032a5af80443334a35f2267TB","batchName":"Test 2",},{"_id":"6032a5b080443334a35f2239","batch_id":"6032a5af80443334a35f2267TB","batchName":"Test 2",},{"_id":"6032a5b080443334a35f2234","batch_id":"6032a5af80443334a35f26467JC","batchName":"Test 3",}]}]

db.collection.aggregate([{$project:{batchData:{batch_id:"$List.batch_id",},},},{$unwind:"$batchData.batch_id"},{$group:{_id:"$_id",batchData:{$addToSet:"$batchData"},},},])