我在使用C#中Treeview与解析XML遇到的问题！[1]

近日我在用C#将PDM中相关内容导入到TreeView的过程中，遇到一个很奇怪的问题，请各位大虾指点，谢谢！

private void ReadXml(string strFileName)
  {
   try
   {
         XmlDocument xmlDoc = new XmlDocument();
         xmlDoc.Load("c:\xxx.pdm");
         TreeNode rootNode = new TreeNode("PDM原始文档结构");
         trvXML.Nodes.Clear();
         this.trv_end.Nodes.Clear();
         tn_end2=new TreeNode("PDM表结构");
         trv_end.Nodes.Add(tn_end2);
         XmlNodeList rootList = xmlDoc.ChildNodes;
         foreach(XmlNode xmlnode in rootList)
         {
               TreeNode tn = new TreeNode(xmlnode.Name);
               if (xmlnode.HasChildNodes)
               {
                     rootNode.Nodes.Add(tn);
                     AnalyseXML(xmlnode, tn);
               }
         }
   
         this.trvXML.Nodes.Add(rootNode);
   }
   catch(Exception ex)
   {
         MessageBox.Show(ex.Message);
   }
   
  }

private void AnalyseXML(XmlNode node, TreeNode tnode)
  {
   try
   {
    XmlNodeList xnlAll = node.ChildNodes;
    TreeNode tn_end=new TreeNode();
    TreeNode tn=new TreeNode();
    string strChineseName="";
    bool TagFlag=false;
    bool TagFlag2=false;
    foreach(XmlNode snode in xnlAll)
    {
     //形成PDM原始文档功能树
     if(snode.NodeType==XmlNodeType.Text)
     {
      tn = new TreeNode(snode.Value+"["+snode.NodeType.ToString()+"]");
     }
     else
     {
      tn=new TreeNode(snode.Name+"("+snode.NodeType.ToString()+")");
     }
     //形成PDM原始文档功能树完毕
     //填充PDM表结构功能树
     if(snode.NodeType==XmlNodeType.Element&&snode.ParentNode.Name.Equals("o:Table"))
     {
      //获取表中文名
      if(snode.Name.Equals("a:Name"))
      {
       strChineseName=snode.FirstChild.Value;
      }
      //表英文名
      if(snode.Name.Equals("a:Code"))
      { 
       tn_end=new TreeNode(strChineseName+"["+snode.FirstChild.Value+"]",100,100);
       
       this.trv_end.TopNode.Nodes.Add(tn_end);
       this.trv_end.SelectedNode=tn_end;
       tn_end2=tn_end;
       TagFlag=true;
      }
      //表说明
      if(snode.Name.Equals("a:Comment"))
      { 
       TagFlag2=true;
       tn_end.Tag=snode.FirstChild.Value+"["+tn_end.Te