Which kind of vehicle is before the trees?
The vehicle is a train.
   src        edge_attr  dst
0    1   to the left of    6
1    2   to the left of    4
2    4  to the right of    2
3    6           behind    8
4    6  to the right of    1
5    6  to the right of    8
6    7            below    8
7    8      in front of    6
8    8   to the left of    6
9    8            above    7