mshak

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

namespace XmlSerializeDemo
{
    [XmlRoot("TechTree")]
    public class TechCollection
    {
        [XmlAttribute("version")]
        public int Version { get; set; }

        [XmlElement("Tech")]
        public TechItem Item { get; set; }
    }

    public class TechItem
    {
        [XmlAttribute("type")]
        public string Type { get; set; }

        [XmlAttribute("name")]
        public string Name { get; set; }
    }

    internal class Program
    {
        private static void Main(string[] args)
        {
            var e = new TechItem() { Type = "Noraml", Name = "Age 1" };
            var t = new TechCollection() { Version = 5, Item = e };

            Serialize(@".\demo.xml", t);
        }

        private static void Serialize<T>(string path, T obj)
        {
            XmlSerializer serializer = new XmlSerializer(obj.GetType());
            XmlWriterSettings settings = new XmlWriterSettings();
            settings.ConformanceLevel = ConformanceLevel.Document;
            settings.OmitXmlDeclaration = false; // не подавлять xml заголовок
            settings.Encoding = Encoding.UTF8; // кодировка
            settings.Indent = true; // добавлять отступы
            settings.IndentChars = "    "; // сиволы отступа

            // подавляем неймспейсы
            XmlSerializerNamespaces dummyNSs = new XmlSerializerNamespaces();
            dummyNSs.Add(string.Empty, string.Empty);

            using (FileStream fileStream = new FileStream(path, FileMode.Create))
            {
                using (XmlWriter xw = XmlWriter.Create(fileStream, settings))
                {
                    serializer.Serialize(xw, obj, dummyNSs);
                }
            }
        }
    }
}

<?xml version="1.0" encoding="utf-8"?>
<TechTree version="5">
    <Tech type="Noraml" name="Age 1" />
</TechTree>