What is covering the trees?
The air is covering the trees.
    src        edge_attr  dst
0     0  to the right of   12
1     1       covered by   19
2     6  to the right of    9
3     6  to the right of   11
4     6   to the left of   17
..  ...              ...  ...
56   18  to the right of    8
57   18           eating   13
58   18  to the right of   15
59   18   to the left of   17
60   19         covering    1

[61 rows x 3 columns]