What are the trees covering?
The trees are covering the roof.
    src        edge_attr  dst
0     0   to the left of   11
1     1  to the right of    5
2     2               in    7
3     2             near    7
4     3   to the left of   10
5     4  to the right of   12
6     5   to the left of   10
7     5   to the left of    1
8     6       covered by   15
9     6   to the left of   17
10    7            below   16
11    7             near    2
12    8  to the right of   12
13    8               in    9
14   10   to the left of   17
15   10  to the right of    5
16   10  to the right of    3
17   11  to the right of    0
18   11  to the right of   17
19   12   to the left of    4
20   12   to the left of    8
21   12               in    7
22   15               on    1
23   15               on    0
24   15         covering    6
25   17  to the right of    6
26   17  to the right of   10
27   17   to the left of   11