I wouldn't use anything with that type of bark, it can harbor bacteria from fecal matter, and also anything that came with the branch in the first place - you really can't clean it well. The types of branches that I once used were either Madrone, or Manzanita. Their bark is smooth and can easily be cleaned. I didn't have any of the branch on the floor. I'd screw them into the back and sides. Before putting a branch in your cage, you should be able to either lightly bake it in the oven if possible, or soak it for a long time, and them sun-bake it. Fortunately for me, the manzanita and madrone grows well in my area so theirs no need to purchase it.
Something to consider - if you put too many branches, then it makes it difficult when its time for cleaning or trying to get your Boa out. It'll wrap itself around anything it can sometimes.
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