class Table
    {
        public Table() 
        {
        }
        public Table(int _id, int _personID, int? _parentID) 
        {
            id = _id;
            personID = _personID;
            parentID = _parentID;
        }

        public int id;
        public int personID;
        public int? parentID;
    }

    class Program
    {
        static void Main(string[] args)
        {
            List<Table> myArr = new List<Table>();
            myArr.AddRange(new Table[] {new Table(1, 1, null), new Table (2, 1, 1),
                new Table(3, 2, 1), new Table(4, 2, null), new Table(5, 2, 4)});

            var result = from title in myArr
                         join message in myArr on title.id equals message.parentID into tempTable
                         from TitleMessages in tempTable.DefaultIfEmpty()
                         where title.personID == 1
                         where !title.parentID.HasValue
                         select new
                         {
                             MessageID = (TitleMessages == null ? (object)null : (object)TitleMessages.id),
                             TitleID = title.id,
                             PersonID = (TitleMessages == null ? (object)null : (object)TitleMessages.personID)
                         };

            Console.WriteLine("TitleID MessageID PersonID");
            foreach (var t in result)
            {
                Console.WriteLine("{0,4}{1,9}{2,8}", t.TitleID, t.MessageID, t.PersonID);
            }


            
        }
    }