Peter the roots look like human limbs. I see a person sitting down on the RHS and reaching out with a long arm and giant hand to grab the wall. Hoping this is what you saw also, or maybe I should go back on those pills.
Hi Tex-
I definitely agree on the human limbs-particularly that "forearm" looking root that grabs the ground in the lower left. If you look at the image upside down (as it looked under the dark cloth), it looks like that arm is holding on to the top of the image like a rock climber. That tree was definitely a sight to see.