tree sap and most other natural crap that sticks to the paint can be easily removed with a clay bar. In fact, even if you dont have sap and crap, a thorough clay job will really really improve your cars paint. The clay will remove industrial fallout and it will look disgusting if you've never clayed your car before. People always comment my car feels like its brand new because it is so smooth. Clay Magic is a good brand to use. Mothers is okay.
Claying instructions:
Start by using dish washing soap to completely strip your car of wax. Do this all under the shade. After washing with dish soap, work in small sections with a bottle of lubrication (windex works from what i've told, but I use quik detailer) and gently glide the clay over the paint. No scrubbing needed, just spray and make sure tghere is plenty of lubrication. After you are done with a section, rinse it off and start on another. Carefully manipulate the clay so that the dirty stuff is moved and so you can start with a fresh section. If you drop the clay, throw it away. It is useless now. You want to kneed the clay over and over so that way the dirty stuff is not scratching against your paint as you rub tghe clay over the car. After you've done the car, wash the car again and proceed to apply a good quality sealant and then a layer of PURE carnuba wax. Klasses All in One followed by S100 wax (found at local harley dealers) will be beautiful. Good luck.