One stress is on "pen". The other on "tra". This seems very unusual to me since I had the impression that most English words are supposed to be pronounced with one stress only.
closed as off-topic by Mari-Lou A, Chenmunka, Misti, ScotM, Drew Jul 2 '15 at 2:07
This question appears to be off-topic. The users who voted to close gave this specific reason:
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English words often have a primary and a secondary stress, especially when they are long (4 syllables or more). In your example, "pen" has the primary stress, and "tra" has the secondary stress.