Are the trees pulling a cart?
Yes, the trees are pulling a cart.
    src        edge_attr  dst
0     1  to the right of    8
1     1   to the left of    4
2     1        pulled by    7
3     2  to the right of    8
4     4               on    3
5     4  to the right of    1
6     6  to the right of    8
7     7          pulling    1
8     8   to the left of    6
9     8   to the left of    2
10    8   to the left of    1