Accessing a parse tree

[Clarendon]

Hello!

I need a program that accesses a parse tree based on the designated
words (terminals) within the tree. For instance, in:

I came a long way in changing my habit.

(ROOT
  (S
    (NP (PRP I))
    (VP (VBD came)
      (NP (DT a) (JJ long) (NN way))
      (PP (IN in)
        (S
          (VP (VBG changing)
            (NP (PRP$ my) (NN habit))))))


the designated words are "a long way". I need the program to recognize
how many parentheses there are after them. Currently two: NN way)).
Then I need it to see how many parentheses there are before it.
Currently there are two as well: (NP (DT. Then the program should that
the designated wordssee are followed by (PP (IN in) and then by  (S
(VP (VBG.

I looked at the NLTK Tree class but it does not seem to have a method
that works with designated words. Is there some kind of tree navigator
that does something like this? If I need to write one myself, I would
appreciate any tips about where to start.

Thanks.