db={"shopproducts":[{"_id":ObjectId("5e9a21868ed974259c0da402"),"shopId":"5e975cc7be7c1b546b7abb17","shopType":"Medium Store","products":[{"isPackedProduct":true,"_id":ObjectId("5e92ff706af877294d63098e"),"brand":"ABC","category":"CAT1","productName":"P1","subCategory":"SUB1"},{"isPackedProduct":true,"_id":ObjectId("5e92ff706af877294d63098e"),"brand":"ABC","category":"CAT1","productName":"P1","subCategory":"SUB1"},{"isPackedProduct":true,"_id":ObjectId("5e92ff706af877294d63098f"),"brand":"EFG","category":"CAT1","productName":"P2","subCategory":"SUB2"},{"isPackedProduct":true,"_id":ObjectId("5e92ff706af84d630977298f"),"brand":"EFG","category":"CAT2","productName":"P3","subCategory":"SUB1"}]}]}

db.shopproducts.aggregate([{$unwind:"$products"},{$group:{_id:{_id:"$_id",shopId:"$shopId",category:"$products.category",subCategory:"$products.subCategory"},products:{$push:"$products"}}},{$group:{_id:{_id:"$_id._id",shopId:"$_id.shopId",category:"$_id.category"},products:{$push:{k:"$_id.subCategory",v:{products:"$products"}}}}},{$group:{_id:{_id:"$_id._id",shopId:"$_id.shopId"},products:{$push:{k:"$_id.category",v:{$arrayToObject:"$products"}}}}},{$replaceRoot:{newRoot:{$mergeObjects:[{_id:"$_id._id",shopId:"$_id.shopId"},{$arrayToObject:"$products"}]}}}])