What is the sign in front of?
The sign is in front of the tree.
   src        edge_attr  dst
0    0           behind    1
1    0      in front of    2
2    1      in front of    0
3    2           behind    0
4    3  to the right of    6
5    3   to the left of    5
6    5  to the right of    3
7    5  to the right of    6
8    6   to the left of    5
9    6   to the left of    3