public class ToTree<T> where T : IToTreeModel

{

    public static List<T> ToDo(List<T> models)

    {

        var dtoMap = new Dictionary<int, T>();

        foreach (var item in models)

        {

            dtoMap.Add(item.Id, item);

        }

        List<T> result = new List<T>();

        foreach (var item in dtoMap.Values)

        {

            if (item.ParentId == )

            {

                result.Add(item);

            }

            else

            {

                if (dtoMap.ContainsKey(item.ParentId))

                {

                    dtoMap[item.ParentId].AddChilrden(item);

                }

            }

        }

        return result;

    }

}

public interface IToTreeModel

{

    int Id { get; set; }

    int ParentId { get; set; }

    List<IToTreeModel> children { get; set; }

    void AddChilrden(IToTreeModel node);

}

    public class ShowMessageUpdatesViewModel: IToTreeModel

    {

        public int Id { get; set; }

        public int ParentId { get; set; }

        public string Name { get; set; }

        public List<IToTreeModel> children { get; set; }

        public void AddChilrden(IToTreeModel node)

        {

            if (children == null)

                children = new List<IToTreeModel>();

            this.children.Add(node);

        }

    }