The pilot of the balloon reported that after three unsuccessful landing attempts during the sightseeing flight, he located a grassy 2-3 acre field and positioned the balloon for landing. He stated that the approach was from the northwest at 500-feet and the balloon was traveling about 6 knots. The pilot anticipated winds near the surface to be from the east; however, after descending to 250-feet the balloon continued in a southerly direction, near trees. The pilot executed a controlled descent over a tree and landed firmly. The basket bounced once and came to rest upright with the balloon's envelope against a tree. After the landing, one of the passengers complained of ankle pain and was transported to a hospital. A medical evaluation revealed that the passenger's ankle was fractured. The pilot reported that a passenger landing briefing was completed prior to landing.