[{"_id":"act_8347100017075469","firstName":"Akki","lastName":"Dlast","accountNumber":"12397124","feature":{"feature-name1":{"baseCode":"bc1","serviceCode":[/**numb of elements & name of elements in servicesCodes are dynamic*/"SC1","SC2","SC3"]},"feature-name2":{"baseCode":"bc2","serviceCode":[/**numb of elements & name of elements in servicesCodes are dynamic*/"SC21","SC22"]},"feature-name3":{"baseCode":"bc3","serviceCode":["SC41","SC42","SC43"]}}}]

db.collection.aggregate([{$match:{"feature.feature-name1.baseCode":{$exists:true}}},{$project:{accountNbr:1,"feature":"feature-name1","baseCode":"$feature.feature-name1.baseCode"}}])