We regularly give fresh apple and willow tree branches to the rabbits as they love to strip off the bark and it gives them a back-to-basics natural activity that keeps them stimulated and happy. It just so happens we have two such trees in the garden and thanks to JB Tree Services we now have a big pile of branches to keep us going for a while! I can thoroughly recommend this company (no, I am not being paid to say this) as not only were they competitively priced but they also were really friendly, efficient and tidy, and were happy to cut up the branches to lengths that would fit in the rabbit pens. If you have any tree work that needs doing, do give them a try: jb-treeservices.co.uk
Before giving branches to rabbits or guinea pigs, make sure that the tree species is safe for eating, as not all trees are. You will find a comprehensive list on the internet. Also make sure that the tree has not been treated with a pesticide or other treatment as this may affect the health of the rabbit or guinea pig.