Was working in ATTI mode just doing circles in the sky in the park. I wasn't watching the altitude as carefully as I should and I was too low for the tree. Just happened to be a policeman around who happened to have a friend in the local Fire Department. They happened NOT to be too busy and they were worried it might drop on some poor unsuspecting soul's head so they retrieved it. For public safety and for me. They were wonderful. I was ashamed. They laughed at me saying don't worry about it. But I'm going to buy the firehouse lunch on Monday. What did I learn? Gotta watch. All the time. And give plenty of clearance. All the time.