According to the flight instructor, he and the private pilot under instruction filled the fuel tanks, performed a preflight inspection, taxied to the runway and completed an engine run up. They began the takeoff roll, with the flaps set at 10 degrees, from the 3,000-foot-long,up-sloped, turf runway and the airplane became airborne about one-third down the runway. The airplane climbed slowly and the flight instructor realized that it would not be able to clear the trees at the end of the runway. The private pilot applied the left rudder in order to turn the airplane and stay clear of the trees, but soon the instructor took the flight controls because he realized that the airplane was going to impact the trees. The airplane struck the trees approximately 20 feet from the tops, impacted the ground, and came to rest inverted. During the accident sequence, the fuselage, wings, and empennage were substantially damaged. The flight instructor reported there were no preexisting mechanical anomalies with the airplane. Weight and balance calculations revealed that the airplane was at or slightly over the maximum takeoff weight provided by manufacturer. Also, the owner's manual stated that the best rate of climb was with flaps up and that the "use of 10 degrees of flaps is reserved for minimum ground runs or for take-off from soft or rough fields with no obstacles ahead."