Safe fro bunny to eat
There are many plants that are safe for your rabbit to eat. I cannot find any information specific to the Liquidambar tree, other than it being fairly resistant to damage from wild rabbits. You may want to consult with your rabbit's veterinarian to see if they have a specific recommendation. It appears that wild rabbits will consume the young plant so it may be safe. If you choose to provide it, introduce it slowly and make sure to observe your rabbit consuming any new food items.
You may also consult a list like this of safe plants for your rabbit: http://www.raising-rabbits.com/pet-safe-plants.htm
Obviously, these lists are not all inclusive. There is limited information published on which plants are safe for rabbits. If you have any specific concerns and cannot find information that it is safe, I would opt to avoid the plant and err on the side of safety.