To get tree sap off of indoor wood furniture, try using a commercial product such as Goo Gone, Goof Off or WD-40. For a homemade solution, you can try using vegetable oil or mayonnaise. Rub the cleaning product gently into the stain to loosen it, let it sit for a few minutes, then wipe off (or follow the manufacturer's directions). If this doesn't work, you can try using mineral spirits. Remember to always test a cleaning product in an inconspicuous are first.