What's the skier pulling?
The skier is pulling the tree.
    src        edge_attr  dst
0     0   to the left of    5
1     0   to the left of    9
2     1            above    3
3     2   to the left of    5
4     2   to the left of    9
5     2   to the left of    4
6     4  to the right of    2
7     4        pulled by    7
8     4  to the right of    7
9     5  to the right of    2
10    5  to the right of    0
11    6   to the left of   12
12    6  to the right of   11
13    7          holding    5
14    7          holding    2
15    7          pulling    4
16    7   to the left of    4
17    9  to the right of    0
18    9  to the right of    2
19   11   to the left of    6
20   12  to the right of    6