I am pleased to tell you that we have had a positive response to the letter.
( I ( ( am ( pleased ( to ( ( tell you ) ( that ( we ( have ( ( had ( a ( positive response ) ) ) ( to ( the letter ) ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (PRP I)) (VP (VBP am) (ADJP (JJ pleased) (S (VP (TO to) (VP (VB tell) (NP (PRP you)) (SBAR (IN that) (S (NP (PRP we)) (VP (VBP have) (VP (VBN had) (NP (DT a) (JJ positive) (NN response)) (PP (TO to) (NP (DT the) (NN letter)))))))))))) (. .)))
We have had a positive response to the letter because we include drugs in the envelope. 
( We ( ( have ( ( ( had ( a ( positive response ) ) ) ( to ( the letter ) ) ) ( because ( we ( include ( drugs ( in ( the envelope ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (PRP We)) (VP (VBP have) (VP (VBN had) (NP (DT a) (JJ positive) (NN response)) (PP (TO to) (NP (DT the) (NN letter))) (SBAR (IN because) (S (NP (PRP we)) (VP (VBP include) (NP (NP (NNS drugs)) (PP (IN in) (NP (DT the) (NN envelope))))))))) (. .)))