What are the trees behind the airplane covered with?
The trees are covered with snow.
    src        edge_attr  dst
0     0  on the front of    7
1     0  to the right of   13
2     0   to the left of    5
3     0  to the right of   11
4     0  to the right of    9
5     1     covered with    8
6     2               on   14
7     4               in    8
8     5           behind    7
9     5       covered by    8
10    5  to the right of    0
11    5     covered with    8
12    5  to the right of   11
13    5  to the right of    7
14    6   to the left of    9
15    7   to the left of    5
16    7            above   12
17    7      in front of    5
18    9   on the side of    7
19    9   to the left of    0
20    9  to the right of    6
21    9   to the left of   11
22   10   on the side of    7
23   11   to the left of    0
24   11   to the left of    5
25   11  to the right of    9
26   11           inside    7
27   11  to the right of   13
28   13   to the left of    0
29   13   to the left of   11