public OrderBookModel Transform() { var asks = new List <OrderBookEntryModel>(); var bids = new List <OrderBookEntryModel>(); Asks.ForEach(x => asks.Add(x.Transform())); Bids.ForEach(x => bids.Add(x.Transform())); return(new OrderBookModel { Asks = new List <OrderBookEntryModel>(asks), Bids = new List <OrderBookEntryModel>(bids) }); }