It sounds like your kitty reacted to the stress of being placed in an unfamiliar environment with unfamiliar cats. I wouldn't be concerned about the bite, as it really is a natural reaction to that situation. When you do get the cat out of the tree though, you can begin acclimating him to your house again. When you bring a new cat into your home, it's important that you give the cat it's own room at first (I believe someone else already mentioned that) and that you keep him in there with his food, water, litter box, toys, blankets, etc. until he seems comfortable. He should have no contact with other cats in the household other than sniffing them through the crack under the door. Make sure you give the cat plenty of attention. The cat needs time to adjust to a new environment on its own terms, and an entire new house with other cats in it is overwhelming and scary. After a week or two of being kept in his own room, you can decide whether you think the animal is ready to meet the resident cat for brief, supervised visits. Then gradually increase the amount of time the cat is allowed to visit with the resident cat and explore his new home. Consider also limiting the amount of space he has access to when you let him explore your home, and gradually increasing it as he becomes comfortable. Introducing an new cat into your home takes time and patience. Once your cat is well established in your new home, if you decide he is to be an outdoor cat, you can begin letting him into the yard for brief supervised periods until he becomes comfortable.