I'd put up a big horizontal loop strung among the trees however
it will fit. Feed it with at the closest point to the shack with
whatever feedline you have handy through a tuner.
Another option is a vertical loop: a delta (point down) can be hung
between two trees and fed at the bottom with minimum feedline
length. Don't worry about the exact shape: I rigged one loop for a
friend in a rather irregular shape, using one pine tree, a post on the
garage, a fence post, and his chimney. The wires weren't even all
in the same plane, but it worked great. We fed it with 11' of
twinlead at the point where the wire passed over the shack. Actual
length was about 200' - a bit short for a full wave on 80m.
Of course, a dipole over the tops of the tallest pine trees isn't a bad
idea, either. Feed it with open wire line to reduce the losses. You
can afford a lot of wire and a good tuner for the price of a "no
radials required" vertical, and it probably will work better, too.
Good luck! - Dale WB6BYU