What is considered an enemy for an Orc’s Aggressive trait?


Volo’s Guide to Monsters says that you may play an Orc character, which gives you the following trait, amongst others (p. 120):

Aggressive. As a bonus action, you can move up to your speed toward an enemy of your choice that you can see or hear.

My question is: what can be considered as an enemy for this trait to apply?

  1. Anything I want
  2. Any living creature, including non-hostile ones
  3. Only creatures that are hostile to me (actual enemies)

For example, can I choose a tree as my enemy, justifying it by a "Me find tree insult my race, me hate tree, me ANGRY!", and then bonus-move toward said tree?