Very rarely, and not for a birthday.

The bigger question is that given the erotic nature of your transference, and the lack of clarity about his ethics, why are you even considering giving him a gift? You need to restrain yourself in all of your actions if you want any chance to benefit therapeutically from your therapy. Only after you stop pursuing him and challenging the treatment boundaries, will you be at all able to see if he is ethical or not. And if he shows himself unethical, you need to walk away and find another therapist.