How to remove sub folders without any files then parent folders if their sub folders and themselves do not contain any files

Question

I have a slightly modified codes to populate my treeView1 with only .PDF files. It works well, except it leaves with many empty folders. Is it a way to remove these folders?

  private void Begin()
    {
        treeView1.Nodes.Clear();
        if (Directory.Exists(FilePath))
            LoadDirectory(FilePath);
    }

    public void LoadDirectory(string Dir)
    {
        DirectoryInfo di = new DirectoryInfo(Dir);
        TreeNode tds = treeView1.Nodes.Add(di.Name);
        tds.Tag = di.FullName;
        tds.StateImageIndex = 0;
        LoadFiles(Dir, tds);
        LoadSubDirectories(Dir, tds);
    }

    private void LoadSubDirectories(string dir, TreeNode td)
    {
        // Get all subdirectories  
        string[] subdirectoryEntries = Directory.GetDirectories(dir);
        // Loop through them to see if they have any other subdirectories  
        foreach (string subdirectory in subdirectoryEntries)
        {
            DirectoryInfo di = new DirectoryInfo(subdirectory);
            TreeNode tds = td.Nodes.Add(di.Name);
            tds.StateImageIndex = 0;
            tds.Tag = di.FullName;
            LoadFiles(subdirectory, tds);
            LoadSubDirectories(subdirectory, tds);
        }
    }


    private void LoadFiles(string dir, TreeNode td)
    {
        string[] Files = Directory.GetFiles(dir, "*.PDF");
        // Loop through them to see files
        foreach (string file in Files)
        {
            FileInfo fi = new FileInfo(file);
            TreeNode tds = td.Nodes.Add(fi.Name);
            tds.Tag = fi.FullName;
            tds.StateImageIndex = 1;
        }
    }