Two things you should try for removing tree sap. One is baby oil, this will soften the sap and emulsify it to make is easy to remove.
Another product that works very well with large surface contamination and gunk is 3M General Purpose Adhesive Remover #08984. This stuff is usually available at better hardware stores, and you can also get it online at Griots Garage.
After the sap is removed, it is best to smooth out the paint surface with Meguires Swirl Remover 2.0. This is very fine polish/filler that will level out any paint irregularities that the sap created in the paint.
Lastly is paint protection to keep the sap from sticking to the surface next time around.
For that, I recommend a product that is from the aviation industry and is available online called "Rejex". It is used instead of wax and is a polymer coating that is applied as a cream. It is allowed to dry, wiped off, and then let cure for 8 hours out of the sun and in temperatures less than 85F.
Rejex is great in that the surface that it cures to is extremely slippery, and stuff does not stick to it. I put it on the windshield and rims as well. It keeps bugs from sticking to the car when they hit it, and helps keep brake dust to a minimum on the rims.
The big plus is that it makes the car more slippery, and can help gas mileage. On boats and airplanes it can add 5-10 kts of top end. One coating will last 3-6 months depending on how adverse the conditions it is used in.
Order it from here