It's the sudden stop that kills you.

Trouble with the treetops is that the aircraft probably won't stay there - especially in pine forest where the tops are pointy and well spaced. It will free fall some distance and then stop suddenly. If the trees are short, it won't be a long fall. If it's mature forest, it'll be a long fall.

I'd pick the water. (says the PP-SEL and former Glider Flight Instructor)

I've seen a glider landed in treetops (pilot with head up his you-know-where ran out of altitude on downwind leg) and the aircraft stayed there. Old deciduous trees in Virginia. Pilot shinnied down the tree. Glider was retrieved with a huge crane with nearly no damage (but glider speeds are very slow).