root root 9 9 r3 r3 S 3 21 22 23 24 25 26 27 28 29 T r4 r4 S 4 12 13 14 15 16 17 18 19 20 T 5 5 r1 r1 S 1 T r2 r2 S 2 T S 6 7 8 10 11 T