1 [M],[M]

     2 [],[]

     3 [M],[M]

     4 [],[]

     5 null

     6 [M],[M]

     7 null

     8 [M],[M]

     9 null

    10 null

    11 M

    12 null

    13 ^

    14 [M],[M]

    15 null

    16 [M],[M]

    17 null

    18 null

    19 M

    20 null

    21 ^