The pilot stated that he attempted to land on a grass airstrip that was about 1,000 feet long. He stated that the airplane touched down about mid-field, and he was unable to stop the airplane before it collided with a tree at the end of the airstrip. The left landing gear support structure was torn from the airplane, and the fuselage was damaged. The pilot stated that his approach was 'too high and hot' and he did not realize that the grass on the airstrip was wet, causing a decrease in the airplane's braking effectiveness. No preimpact mechanical malfunction was reported.