What are the trees on the hill covering?
The trees are covering the tunnel.
    src        edge_attr  dst
0     0   to the left of   13
1     0   to the left of    5
2     0   to the left of    3
3     2   to the left of   13
4     2   to the left of   11
5     3               in    5
6     3  to the right of    0
7     4               on    0
8     4         covering   11
9     4           behind   13
10    5  to the right of    0
11    6           riding   13
12    6               on   13
13    6               at    1
14    7  to the right of   13
15    7  to the right of   10
16    8  to the right of   10
17    8  to the right of   13
18    9  to the right of   10
19   10   to the left of    9
20   10   to the left of    7
21   10   to the left of    8
22   11  to the right of    2
23   11   to the left of   13
24   11       covered by    4
25   12   to the left of   13
26   13         entering   11
27   13      in front of    4
28   13  to the right of    2
29   13  to the right of    0
30   13  to the right of   11
31   13   to the left of    8
32   13   to the left of   15
33   13   to the left of    7
34   13  to the right of   12
35   14               on    4
36   15  to the right of   13