On December 15, 2018, about 1420 central standard time, an amateur-built Sonex airplane, N393SX, collided with a tree and terrain while on final approach to Lodi Lakeland Airport (9WN5), near Lodi, Wisconsin. The sport pilot sustained serious injuries, and the airplane was substantially damaged. The airplane was owned by the pilot and operated under Title 14 Code of Federal Regulations (CFR) Part 91 as a personal flight without a flight plan. Day visual meteorological conditions prevailed for the local flight that departed 9WN5 about 1340.The pilot reported that he entered the left downwind leg for runway 9 with the intention to make a full-stop landing. He stated that his turn from the downwind leg to base leg was uneventful; however, the airplane's airspeed had increased slightly during the base leg. The pilot reported that he turned onto final approach about ½ mile from the end of the runway at 1,600 ft mean sea level (about 750 ft above the ground) and reduced airspeed to about 63 mph. The pilot stated that while he focused on maintaining proper landing airspeed the airplane drifted north of the extended runway centerline and the airplane's left wingtip collided with a treetop about 50-60 ft above the ground. The airplane subsequently spun around the tree and descended about 60° nose-down into the ground. The pilot stated that the airplane did not bounce upon impact with the ground. The pilot reported that there were no preimpact mechanical malfunctions with the airplane that would have precluded normal flight. The pilot stated that he was fixated with maintaining his airspeed during final approach and that he inadvertently allowed the airplane to drift north of the final approach course and into the tree.