Возникла ошибка при отражении типа - C#

   public class TW
    {   
        [XmlAttribute]
        public string Name;
        [XmlArrayAttribute]
        public P[] Parent;
        public void ShowMe()
        {
            Console.WriteLine("{0}", Name);
            foreach (P p in Parent)
                p.ShowMe();
        }
    }
    public class P
    {
        [XmlAttribute]
        public string Name;
        [XmlAttribute]
        public string Text;
        [XmlAttribute]
        public string Type;
        [XmlAttribute]
        public string Path;
        [XmlArrayAttribute]
        public C[] Node;
        public void ShowMe()
        {
            Console.WriteLine("{0} {1} {2} {3}", Name, Text, Type, Path);
            foreach (C c in Node)
                c.ShowMe();
            
        }
    }
    public class C
    {
        [XmlAttribute]
        public string Name;
        [XmlAttribute]
        public string Text;
        public void ShowMe()
        {
            Console.WriteLine("{0} {1}",Name,Text);
        }
    }
    [Serializable]
    public class TP
    {
        [XmlAttribute]
        public string Name;
        [XmlAttribute]
        public string Descr;
        [XmlAttribute]
        public TW TreeView;
        public void ShowMe()
        {
            Console.WriteLine("{0} {1}", Name, Descr);
            TreeView.ShowMe();
        }
    }
    public class GUI
    {
        public GUI(XElement xe)
        {
            TP tp = new TP();
            XmlSerializer serializer = new XmlSerializer(typeof(TP));
            TextReader tr=new StringReader(xe.ToString());
            tp=(TP)serializer.Deserialize(tr);
            tp.ShowMe();
        }
 
    }
    class Program
    {
        static void Main(string[] args)
        {
            GUI g=new GUI(XDocument.Load("1.xml").Element("TabPage"));
        }
    }