You can remove dried tree sap from a car by using some mineral spirits or some nail polish remover.
Take a rag or sponge and add either some nail polish remover or some mineral spirits to the rag or sponge and then gently scrub the dried tree sap from the car.
It may take a few tries and you might need to soak a rag and lay the soaked rag with the nail polish remover or mineral spirits and let it sit on the tree sap for 20 minutes or so and then the dried tree sap should start coming off.
Then you should be able to just wash the dried tree sap off.
If the tree sap hasn't dried yet then using some Purple Power Degreaser or other degreaser usually works good but if it has dried then the nail polish remover or the mineral spirits will work at removing the dried tree sap safely.
Lighter fluid that you use for charcoal grills can also work good at removing dried tree sap from your vehicle without damaging it.