What is on the tree?
The leaves are on the tree.
    src        edge_attr  dst
0     0  to the right of    2
1     0               on    5
2     1               on    9
3     1  to the right of   12
4     2   to the left of    7
5     2   to the left of    0
6     2  to the right of    5
7     2   to the left of    8
8     3  to the right of    5
9     3   to the left of    8
10    3   to the left of    7
11    4   to the left of    7
12    4   to the left of    8
13    5   to the left of    2
14    5   to the left of    8
15    5   to the left of   10
16    5   to the left of   17
17    5   to the left of    3
18    6  to the right of   14
19    7  to the right of    2
20    7  to the right of   17
21    7  to the right of    4
22    7               on    8
23    7  to the right of    3
24    8  to the right of   16
25    8  to the right of    3
26    8  to the right of    2
27    8  to the right of    4
28    8  to the right of   17
29    8  to the right of    5
30    9  to the right of   11
31    9  to the right of   12
32   10  to the right of    5
33   11   to the left of    9
34   11               on   12
35   11   to the left of   12
36   12  to the right of   11
37   12   to the left of    1
38   12   to the left of    9
39   14   to the left of    6
40   16   to the left of    8
41   17   to the left of    7
42   17  to the right of    5
43   17   to the left of    8