What are the trees on?
The trees are on the branch.
    src        edge_attr  dst
0     1  to the right of   11
1     1  to the right of   13
2     2               on   15
3     2   to the left of    6
4     3               on    6
5     3  to the right of   11
6     3  to the right of    7
7     4   to the left of    9
8     4  to the right of    7
9     4  to the right of   11
10    5  to the right of    7
11    5  to the right of   11
12    5   to the left of    9
13    6  to the right of    2
14    7   to the left of    3
15    7   to the left of    5
16    7   to the left of    8
17    7   to the left of    4
18    8  to the right of    7
19    8   to the left of    9
20    8  to the right of   11
21    9  to the right of    5
22    9  to the right of    4
23    9  to the right of    8
24    9  to the right of   13
25   10  to the right of   11
26   11   to the left of    1
27   11   to the left of    8
28   11   to the left of    4
29   11   to the left of    5
30   11   to the left of   13
31   11   to the left of    3
32   11   to the left of   10
33   13   to the left of    1
34   13  to the right of   11
35   13   to the left of    9