[{"_id":ObjectId("5f33cc2a1e84082968132324"),"customerId":2196,"productList":[{"productId":7531,"itemList":[{"id":144},{"id":145}]},{"productId":7534,"itemList":[{"id":1244},{"id":1243},{"id":1245},{"id":1242}]}]},{"_id":ObjectId("5f33cc2a1e84082968132326"),"customerId":2201,"productList":[{"productId":101201,"itemList":[{"id":863},{"id":865},{"id":862}]},{"productId":7537,"itemList":[{"id":982},{"id":1002},{"id":896}]}]}]

db.collection.aggregate([{$unwind:"$productList"},{$unwind:"$productList.itemList"},{$sort:{"productList.itemList.id":1}},{$group:{_id:{_id:"$_id",customerId:"$customerId",productId:"$productList.productId"},itemList:{$push:"$productList.itemList"}}},{$sort:{"_id.productId":1}},{$group:{_id:{_id:"$_id._id",customerId:"$_id.customerId"},productList:{$push:{productId:"$_id.productId",itemList:"$itemList"}}}},{$project:{_id:"$_id._id",customerId:"$_id.customerId",productList:1}},{$sort:{customerId:1}}])