What's the tree in front of?
The tree is in front of the bridge.
    src        edge_attr  dst
0     1  to the right of    2
1     1   to the left of    7
2     1   to the left of    6
3     2   to the left of    1
4     2   on the side of    3
5     3               on    4
6     3            above    4
7     4           behind    6
8     4            under    3
9     6      in front of    4
10    6               by    4
11    6  to the right of    1
12    7  to the right of    1
13    7   on the side of    3
14    7               of    3