I do a bit of rock climbing too. For that, I have a Black Diamond big wall harness. I also do technical rope and confined space rescue, so I have a Yates, class III, rescue harness with SUPER wide padding on the legs and waist. My New Tribe Tengu tree climbing saddle makes those other harnesses feel like I just have rope wrapped around me! Tree climbing saddles are Sooooooooo comfortable.

You CAN use a rock harness in the trees, but you won't enjoy it much after you've been hanging for an hour or so. Tiny webbing and padding equals big pain in the legs and waist.