How to recursively check folder and its subfolder

public void FindFiles(string startDir, string fileName)
       {


           if (Directory.Exists(startDir))
           {
             string[] files = Directory.GetFiles(startDir,      fileName,SearchOption.AllDirectories);

               if (files.Length > 0)
               {
                   foreach (string file in files)
                   {
                       resultsList.Items.Add(file);//Add to a Listview or whatever
                   }


               }
           }


       }