Here are two parse trees for string dcdcd.

                S                           S
               /|\                         /|\
              / | \                       / | \
             S  c  S                     S  c  S
            /|\    |                     |    /|\
           / | \   d                     d   / | \
          S  c  S                           S  c  S
          |     |                           |     |
          d     d                           d     d