Tying a wrench or clevis pin or screw link that weighs about 10-16 oz. to some string line, maybe from a kite or contractors string line may help. Through that through a crotch in the upper canopy. You want to get the line through a crotch at least 2/3 the height of the tree if possible.. Use that pilot line to pull through a stronger rope.. Arborist ropes tend to run around 7,000 lbs tensile, so look for something as close to that as possible... clothes line isn't going to do you much good in hurricane force winds..
Then either send up a running bowline if you can isolate the line (no interfering branches).. or you can use a fishing pole style tie off, where the end of the rope runs through the crotch down the tree and is tied off to the base of the tree.
You'll be looking for an anchor point (the other tree that your're tying off to), to be at 45º angleor more level if possible. If you can use multiple lines then that's all the better.. good luck with it