They are living things. We shouldn't seek to deliberately cause pain if possible. While I like how stuff like bonsai trees look, I also feel a bit bad for them, wired and snipped in so many places and forced to be grown unnaturally small.

Or people who deliberately carve graffiti into trees with a knife.

Plants and trees have interestingly complex communication networks. We barely understand their microfauna and underground microbiomes that allow forests to grow much healthier and disease-resistant than our backyards. I have a funny feeling we know a lot less than we think we know, like when scientists discovered that babies can actually feel pain, or that dogs realize when they are treated unfairly. Stuff discovered within our lifetimes, lol.