The private pilot was landing at a remote airstrip surrounded by trees at the completion of a Title 14, CFR Part 91 personal flight. The pilot stated that during the approach, just before touchdown, he allowed the airplane to drift left of his intended approach path, and the left main landing gear wheel struck a tree, which yawed the airplane to the left. During touchdown, the right main landing gear collapsed, followed by the collapse of the left main landing gear. The airplane sustained substantial damage to the wings, fuselage and empennage. The pilot stated that there were no preaccident mechanical problems with the airplane.