[{"_id":null,"generic_name":"Ademetionine","form_name":"Tablets-MD","dose_size":"400MG","subcategory_name":"Others","brand1":[{"brand_name":"CARTISURE 400 MG TAB","manufacturer_name":"Zoic Lifesciences"},{"brand_name":"ADENORICH 400 MG TAB","manufacturer_name":"Future Pharma Pvt Ltd"},{"brand_name":"ENSAME 400 TAB","manufacturer_name":"ICARUS HEALTHCARE"}],"id":1}]

db.collection.aggregate([{$project:{brand_name_1:{"$concat":[{$arrayElemAt:["$brand1.brand_name",0]},"(",{$arrayElemAt:["$brand1.manufacturer_name",0]},")"]},brand_name_2:{"$concat":[{$arrayElemAt:["$brand1.brand_name",1]},"(",{$arrayElemAt:["$brand1.manufacturer_name",1]},")"]},brand_name_3:{"$concat":[{$arrayElemAt:["$brand1.brand_name",2]},"(",{$arrayElemAt:["$brand1.manufacturer_name",2]},")"]},sub_category:"$subcategory_name",strength:"$dose_size",form:"$form_name",molecule:"$generic_name",id:1,_id:0}}])