How to Create and Append XML Node ?

  public void createXML()
    {
        XmlDocument doc = new XmlDocument(); 
        string filename="c:\\sample.xml";
        XmlTextWriter tw=new XmlTextWriter(filename,null);
        tw.Formatting=Formatting.Indented;
        tw.WriteStartElement("Author");
        tw.WriteElementString("ID","1");
        tw.WriteElementString("SubmissionDate","1-1-08");
        tw.WriteElementString("Topic","test");
        tw.WriteElementString("Title","test");
        tw.WriteStartElement("Authors");
        tw.WriteStartElement("Author");
        tw.WriteElementString("Name","XYZ");
        tw.WriteElementString("Affiliation","ABC");
        tw.WriteEndElement();
        tw.WriteEndElement();
        tw.WriteElementString("Summary","Hi");
        tw.WriteElementString("Text","Hello");
        tw.WriteEndElement();			
        tw.Flush();
        tw.Close();
        StreamReader srXml = new StreamReader(filename);
        string xmlFile = srXml.ReadToEnd()
    }

XmlDocument doc = new XmlDocument();
doc.LoadXml(xmlFileString);
XmlNode root = doc.DocumentElement;
XmlElement element = doc.CreateElement("TestNode");
element.InnerText="test";
root.AppendChild(element);
doc.Save(Console.Out);