How do you deal with silly interview questions?

First, don't panic. Pause and take a deep breath. Then remind yourself that there's no "right" answer to these questions. The job isn't hinging on whether you choose to be a spruce versus an oak.
construction interviewers usually ask these questions to see how you react under pressure and how well you handle the unexpected. It's not so important what type of tree (or car, or animal) you choose as that you explain your choice in a way that makes you look favorable.