If I'm not mistaken there is a filesystemdatasource control that you can use. I think you can specify the depth you're intrested in.

Check the sdk.

Or make your own function

void GetAllFiles(UnifiedDirectory start, List<UnifiedFile> files)
{

    foreach (UnifiedFile file in start.GetFiles())
    {
        files.Add(file);
    }
    foreach (UnifiedDirectory dir in start.GetDirectories())
    {
        GetAllFiles(dir, files);
    }
}