It depends; if you know what the data looks like in advance, then fine -
use XmlSerializer to read the xml into your class structure. But this
won't work for ad-hoc xml.

Example below - is this what you had in mind? If not - please explain
what you do want...

using System;
using System.Collections.Generic;
using System.IO;
using System.Text;
using System.Xml;
using System.Xml.Serialization;
[Serializable]
public sealed class TreeNode
{
    [XmlAttribute]
    public string Key { get; set; }
    [XmlAttribute]
    public string Text { get; set; }

    private List<TreeNode> nodes;

    public List<TreeNode> Nodes
    {
        get
        {
            if(nodes == null) nodes = new List<TreeNode>();
            return nodes;
        }
    }

    public override string ToString()
    {
        return Text;
    }
}

static class Program {
    static void Main() {
        TreeNode tree = new TreeNode {
            Key = "A", Text = "Foo",
            Nodes = {
                new TreeNode
                {
                    Key = "B", Text = "Bar",
                    Nodes = {
                        new TreeNode {
                            Key = "C", Text = "Blip"
                        }
                    }
                },
                new TreeNode {
                    Key = "D", Text = "Blop"
                }
            }
        };
        StringBuilder sb = new StringBuilder();
        XmlSerializer xser = new XmlSerializer(typeof(TreeNode));
        using (XmlWriter writer = XmlWriter.Create(sb))
        {
            xser.Serialize(writer, tree);
            writer.Close();
        }

        string xml = sb.ToString();
        Console.WriteLine(xml);

        using (XmlReader reader = XmlReader.Create(new StringReader(xml)))
        {
            TreeNode backAgain = (TreeNode) xser.Deserialize(reader);
        }
    }
}