The accident occurred at about 6:20 p.m. in front of 375 Route 25A, just east of Kings Park High School.
Police say Anna Devecchis, 49, was driving a 2013 Nissan Rogue west when her vehicle veered off the roadway and struck the tree.
Devecchis was transported via Suffolk County Police helicopter to Stony Brook University Hospital where she was pronounced dead.
The vehicle was impounded for a safety check and the investigation is continuing. Police are asking anyone with information on the crash to contact the Fourth Squad at 631-854-8452.