怎么样自动添加xml子节点

<?xml version="1.0" encoding="utf-8" ?> 
- <siteMapNode url="default.aspx" title="新书推荐" description="">
  <siteMapNode title="C#" url="BookList.aspx?typeid=1" description="" /> 
  <siteMapNode title=".NET" url="BookList.aspx?typeid=25" description="" /> 
  <siteMapNode title="ASP.NET" url="BookList.aspx?typeid=29" description="" /> 
  <siteMapNode title="Basic VB VB Script" url="BookList.aspx?typeid=16" description="" /> 
  <siteMapNode title="C C++ VC VC++" url="BookList.aspx?typeid=15" description="" /> 
  <siteMapNode title="CSS Div" url="BookList.aspx?typeid=4" description="" /> 
  <siteMapNode title="ddd" url="BookList.aspx?typeid=44" description="" /> 
  <siteMapNode title="HTML XML" url="BookList.aspx?typeid=22" description="" /> 
  <siteMapNode title="J2EE" url="BookList.aspx?typeid=2" description="" /> 
  <siteMapNode title="Java Script Java" url="BookList.aspx?typeid=21" description="" /> 
  <siteMapNode title="JSP" url="BookList.aspx?typeid=31" description="" /> 
  <siteMapNode title="Perl" url="BookList.aspx?typeid=26" description="" /> 
  <siteMapNode title="WINDOWS" url="BookList.aspx?typeid=35" description="" /> 
  <siteMapNode title="电子商务" url="BookList.aspx?typeid=38" description="" /> 
  <siteMapNode title="计算机等级考试" url="BookList.aspx?typeid=17" description="" /> 
  <siteMapNode title="计算机理论" url="BookList.aspx?typeid=20" description="" /> 
  <siteMapNode title="其他" url="BookList.aspx?typeid=28" description="" /> 
  <siteMapNode title="网站开发" url="BookList.aspx?typeid=27" description="" /> 
  </siteMapNode>
我 想写一个类自动网上面的xml文件里添加子节点，求高人指点一二