db={"collection":[{"_id":ObjectId("5bed8391f255307d51f344c3"),"serviceProvider":ObjectId("5bed8367f255307d51f344c1"),"data":"B","wholesaler":[{"item":"1"}]},{"_id":ObjectId("5bed83aef255307d51f344c4"),"serviceProvider":ObjectId("5bed8370f255307d51f344c2"),"data":"C","wholesaler":[{"item":"2"}]},{"_id":ObjectId("5bed83f4f255307d51f344c5"),"serviceProvider":ObjectId("5bed8370f255307d51f344c3"),"data":"D","wholesaler":[{"item":"3"}]}],"other":[{"_id":ObjectId("5bed8367f255307d51f344c1"),"name":"A"},{"_id":ObjectId("5bed8370f255307d51f344c2"),"name":"B"}]}

db.collection.aggregate([{$unwind:"$wholesaler"},{$lookup:{from:"other",localField:"serviceProvider",foreignField:"_id",as:"serviceProvider"}},{$unwind:{path:"$serviceProvider","preserveNullAndEmptyArrays":true}},])