title: java TreeSet - don't remove duplicate items
body: <p>TreeSet removes different items with the same Comprator value. I don't want it be removed.
  Is there any way to control this? Or use another container class?</p>
  
  <p>Added:
  OK. It seems I can't use Set.
  I need insert sorting feature, for performance consideration. Can List do this? Thanks all.</p>