Safe wood

What types of untreated wood are safe for bunnies to chew?

beechwood, branches from fruit trees, like apples and pears, willow
there might be more.
You know they sell these wooden shapes for buns, don't know what wood that is

I'm thinking wood for building a playhouse/hut thing..... that they could safely chew on.

My cousin made a hidy tunnel out of willow sticks.
I often give mine some apple tree twigs and branches.