Where are the trees?
The trees are on the hill.
    src        edge_attr  dst
0     1   to the left of   11
1     1  to the right of   13
2     1  to the right of    6
3     1               on    4
4     3  to the right of    4
5     4   to the left of    3
6     4   to the left of    8
7     6   to the left of    1
8     8  to the right of   14
9     8  to the right of    4
10    9  to the right of   14
11   10  to the right of   11
12   10  to the right of   12
13   11  to the right of    1
14   11   to the left of   10
15   12   to the left of   10
16   13   to the left of    1
17   13               by    1
18   14   to the left of    9
19   14   to the left of    8
20   14               by    4