Day 7 logic issue?

I think your Day 7 implementation fails to calculate the solution to this input

```
a (1) -> b, c
b (2) -> d1, e1
c (10)
d1 (1) -> d
e1 (1) -> e
e (3)
d (2)
```

which I would expect to be `2` because the tree can be fixed by changing node `d1` to `2`