Worry as only a FurMom can - but take comfort in that he will come down on his own one way or another. If, after 24 hours, he hasn't then call the NON-emergency SPCA # for advice (or your local fire dept. as they have the long ladders!)
On a much, much smaller scale, my cat climbed the bedroom curtains and was perched on the rail, crying his heart out for help getting down. I opened one eye and said, "you got yourself up, you can get yourself down." It was a cathedral ceiling, about 10 feet up. By the time I woke up for real, he was down.
For your cat, hunger, thirst, and other critters-in-the-night are a fantastic incentive to motivate oneself to "branch out" as it were!
ETA: One thing to keep in mind, when he does decide to venture downward, you may hear him flopping from branch to branch, looking like a "Plinko" chip coming down. Do Not Freak Out! Their bodies are quite able to take it.