1: Test for source tree numbering 2: Level A 3: Level B 4: Level B 5: Level C 6: Level B 7: Level C 8: Level D 9: Level A 10: Level B 11: Level C 12: Level D 13: Level E 14: Level A 15: Level B 16: Level C 17: Level D 18: Level E 19: Level D 20: Level E 21: Level C 22: Level D 23: Level B