treeview节点的XML表示

我正在尝试从XML文件导入和导出到treeview。但我有这个问题。 sample treeview 具有同一父节点的一个根节点和两个子节点。我用于导出和导入的代码不起作用。导出treeview时,保存的XML文件如下所示:

<?xml version="1.0" encoding="utf-8" ?>
<AAA>
BBBCCC</AAA>

当我将xml文件导入到treeview时,它如下所示 after import xml to treeview . 我用于导出和导入的代码是:

//Open the XML file, and start to populate the treeview
private void populateTreeview()
{
    OpenFileDialog dlg = new OpenFileDialog();
    dlg.Title = "Open XML Document";
    dlg.Filter = "XML Files (*.xml)|*.xml";
    dlg.FileName = Application.StartupPath + "\\..\\..\\example.xml";

    if (dlg.ShowDialog() == DialogResult.OK)
    {
        try
        {
            //Just a good practice -- change the cursor to a 
            //wait cursor while the nodes populate
            this.Cursor = Cursors.WaitCursor;
            //First, we'll load the Xml document
            XmlDocument xDoc = new XmlDocument();
            xDoc.Load(dlg.FileName);        

            // Now, clear out the treeview, 
            // and add the first (root) node
            treeView1.Nodes.Clear();
            treeView1.Nodes.Add(new TreeNode(xDoc.DocumentElement.Name));

            TreeNode tNode = new TreeNode();
            tNode = (TreeNode)treeView1.Nodes[0];

            // We make a call to addTreeNode, 
            // where we'll add all of our nodes
            addTreeNode(xDoc.DocumentElement, tNode);

            // Expand the treeview to show all nodes
            treeView1.ExpandAll();    
        }
        catch(XmlException xExc) 
        {
            // Exception is thrown is there is an error in the Xml
            MessageBox.Show(xExc.Message);
        }
        catch(Exception ex) //General exception
        {
            MessageBox.Show(ex.Message);
        }
        finally
        {
            this.Cursor = Cursors.Default; //Change the cursor back
        }
    }
}

// This function is called recursively until all nodes are loaded
private void addTreeNode(XmlNode xmlNode, TreeNode treeNode)
{
    XmlNode xNode;
    TreeNode tNode;
    XmlNodeList xNodeList;

    if (xmlNode.HasChildNodes)    // The current node has children
    {
        xNodeList = xmlNode.ChildNodes;

        for(int x = 0; x <= xNodeList.Count - 1; x++) 
        {
            // Loop through the child nodes
            xNode = xmlNode.ChildNodes[x];
            treeNode.Nodes.Add(new TreeNode(xNode.Name));
            tNode = treeNode.Nodes[x];
            addTreeNode(xNode, tNode);
        }
    }
    else //No children, so add the outer xml (trimming off whitespace)
        treeNode.Text = xmlNode.OuterXml.Trim();
}

private XmlTextWriter xr;

public void exportToXml2(TreeView tv, string filename) 
{
    xr = new XmlTextWriter(filename, System.Text.Encoding.UTF8);
    xr.WriteStartDocument();
    //Write our root node
    xr.WriteStartElement(treeView1.Nodes[0].Text);

    foreach (TreeNode node in tv.Nodes)
    {
        saveNode2(node.Nodes);
    }

    //Close the root node
    xr.WriteEndElement();
    xr.Close();
}

private void saveNode2(TreeNodeCollection tnc)
{
    foreach (TreeNode node in tnc)
    {
        // If we have child nodes, we'll write 
        // a parent node, then iterate over
        // the children
        if (node.Nodes.Count > 0)
        {
            xr.WriteStartElement(node.Text);
            saveNode2(node.Nodes);
            xr.WriteEndElement();    
        } 
        else //No child nodes, so we just write the text
        {
            xr.WriteString(node.Text);
        }
    }
}

问题出在哪里?