Treeview node in C sharp

public Form1()
{
    InitializeComponent();

    DirectoryInfo directoryInfo = new DirectoryInfo(@"C:\Users\Shahul\Documents\Visual Studio 2010\Projects\TreeView\TreeView\bin\FileExplorer")
    if (directoryInfo.Exists)
    {
        treeView1.AfterSelect += treeView1_AfterSelect;
        BuildTree(directoryInfo, treeView1.Nodes);
    }
}

private void BuildTree(DirectoryInfo directoryInfo, TreeNodeCollection addInMe)
{
    TreeNode curNode = addInMe.Add(directoryInfo.Name);

    foreach (FileInfo file in directoryInfo.GetFiles())
    {
        curNode.Nodes.Add(file.FullName, file.Name);
    }
    foreach (DirectoryInfo subdir in directoryInfo.GetDirectories())
    {
        BuildTree(subdir, curNode.Nodes);
    }
}

private void treeView1_AfterSelect(object sender, TreeViewEventArgs e)
{
    if(e.Node.Name.EndsWith("txt"))
    {
        this.richTextBox1.Clear();
        StreamReader reader = new StreamReader(e.Node.Name);
        this.richTextBox1.Text = reader.ReadToEnd();
        reader.Close();
    }
}