What is the pattern of the trunks?
The trunks are checkered.
    src        edge_attr  dst
0     0   to the left of    5
1     1   to the left of   10
2     1   to the left of   12
3     2   to the left of    3
4     2   to the left of    9
5     2  to the right of   13
6     2   to the left of    5
7     3  to the right of    2
8     4  to the right of   12
9     4  to the right of    9
10    4  to the right of    5
11    5  to the right of   12
12    5  to the right of    0
13    5   to the left of    4
14    5  to the right of    2
15    6               in    7
16    6   to the left of    8
17    8  to the right of    6
18    9   to the left of    4
19    9  to the right of   12
20    9  to the right of    2
21   10        on top of    3
22   10  to the right of    1
23   12        riding on    5
24   12  to the right of    1
25   12  to the right of   13
26   12   to the left of    5
27   12   to the left of    4
28   12   to the left of    9
29   12        on top of    5
30   13   to the left of   12
31   13   to the left of    2