[{"_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([{"$unwind":"$List"},{$group:{_id:{_id:"$_id",batch_id:"$List.batch_id"},batchName:{$first:"$List.batchName"},count:{$sum:1}}},{$group:{_id:"$_id._id",batchData:{$push:{"batch_id":"$_id.batch_id","batchName":"$batchName","count":"$count"}}}}])