Write XML in memory to XmlDocument

XMLWrite.cs

XmlWriterSettings setting = new XmlWriterSettings();
setting.ConformanceLevel = ConformanceLevel.Auto;
StringBuilder builder = new StringBuilder();

using (XmlWriter writer = XmlWriter.Create(builder, setting))
{
    writer.WriteStartElement("Users");
    foreach (var user in users)
    {
        writer.WriteStartElement("User");
        writer.WriteElementString("ID", user.ID.ToString());
        writer.WriteElementString("Name", user.Name);
        writer.WriteEndElement();
    }
    writer.WriteEndElement();
    writer.Flush();
}

XmlDocument doc = new XmlDocument();
doc.LoadXml(builder.ToString());