public class AssetDTO
    {
        public int AssetID;
        public string AssetName;
        public List<AssetItem> Items;
    }


    public class Asset
    {
        public int AssetID { get; set; }
        public string Name { get; set; }        
    }


    public class AssetItem
    {
        public int AssetItemID { get; set; }
        public int AssetID { get; set; }
    }


 List<Asset> assetList = new List<Asset>();
            assetList.Add(new Asset { AssetID = 1, Name = "One"});
            assetList.Add(new Asset { AssetID = 2, Name = "zzz" });
            assetList.Add(new Asset { AssetID = 3, Name = "xxx" });
           

            List<AssetItem> itemsList = new List<AssetItem>();
            itemsList.Add(new AssetItem { AssetItemID = 1, AssetID = 1 });
            itemsList.Add(new AssetItem { AssetItemID = 2, AssetID = 1 });
            itemsList.Add(new AssetItem { AssetItemID = 3, AssetID = 2 });
            itemsList.Add(new AssetItem { AssetItemID = 4, AssetID = 3 });
            itemsList.Add(new AssetItem { AssetItemID = 5, AssetID = 3 });



            var ccc = from a in assetList
                      join b in itemsList on a.AssetID equals b.AssetID
                      select new List<AssetDTO>();