using System;
using System.Collections.Generic;
using System.IO;
using System.Xml.Serialization;

public class Script
{
	public static void Main (string[] args)
	{
	   try
	   {
	   	MyTreeNode node = new MyTreeNode("Root")
				.With(new MyTreeNode("First Child level 1")
					.With(new MyTreeNode("First Child level 2")
						.With(new MyTreeNode())
						.With(new MyTreeNode())
						.With(new MyTreeNode())
					)
					.With(new MyTreeNode("Second Child level 2"))
					.With(new MyTreeNode("Third Child level 2"))
				)
				.With(new MyTreeNode("Second Child level 1"))
				.With(new MyTreeNode("Third Child level 1"))
				;
	   	string xml = MyWebMethodWithStrongTypedArgument (node);
	   	Console.WriteLine(xml);
	   	MyTreeNode node1 = MyWebMethodWithLooselyTypedArgument (xml);
	   	foreach (MyTreeNode mtn in node1.Children) {
		   	Console.WriteLine(mtn.Caption);
	   	}
	   }
	   catch (Exception ex)
	   {
	      Console.WriteLine(ex.ToString());
	   }
	}

	//[WebMethod] in future
	public static string MyWebMethodWithStrongTypedArgument (MyTreeNode node)	{
		return node.Serialize ();
	}
	//[WebMethod] in future
	public static MyTreeNode MyWebMethodWithLooselyTypedArgument (string xml)	{
		return MyTreeNode.Deserialize (xml);
	}
}

[Serializable]
public class MyTreeNode {
	string		_caption;
	List<MyTreeNode>	_children;
	
	[XmlAttribute]
	public string	Caption { get { return _caption; } set { _caption = value; } }
	
	[XmlArrayItem(ElementName= "MyTreeNode", IsNullable=true,   Type = typeof(MyTreeNode))]
	[XmlArray(ElementName="MyTreeNodes")]
	public List<MyTreeNode> Children { get { return _children; } }
	
	public MyTreeNode () {
		_children = new List<MyTreeNode> ();
	}

	public MyTreeNode (string caption): this() {
		_caption = caption;
	}
	
	public MyTreeNode With (MyTreeNode node) {
		if (string.IsNullOrEmpty(node.Caption))
			node.Caption = string.Format("MyTreeNode{0}", _children.Count + 1);
		_children.Add(node);
		return this;
	}
	
	public string Serialize () {
		string ret;
		XmlSerializer xmlFormat = new XmlSerializer(typeof(MyTreeNode));
		Stream ms = new MemoryStream();
		using (StreamReader sr = new StreamReader(ms)) {
			xmlFormat.Serialize(ms, this);
			ms.Position = 0;
			ret = sr.ReadToEnd();
		}
		return ret;
	}
	
	public static MyTreeNode Deserialize (string str) {
		MyTreeNode ret;
			XmlSerializer mySerializer = new XmlSerializer(typeof(MyTreeNode));
			Stream ms = new MemoryStream();
	      using (StreamWriter sw = new StreamWriter(ms)) {
				sw.Write(str);
				sw.Flush();
				ms.Position = 0;
				ret = (MyTreeNode) mySerializer.Deserialize(ms);
			}
		return ret;
	}
}

...
public class MyTreeNode {
	public MyTreeNode[] MyTreeNodes;
	public string Caption;
}
...