Implement practice: tree-building

[problem specification ](https://github.com/exercism/problem-specifications/tree/master/exercises/tree-building)| [description](https://github.com/exercism/problem-specifications/blob/master/exercises/tree-building/description.md) | ~canonical data~

You may find it helpful to follow [this checklist](https://github.com/exercism/javascript/blob/83feda2af955df1ef9f3a8080338f506f0fdf696/CONTRIBUTING.md#new-exercise) from the [CONTRIBUTING.md](https://github.com/exercism/javascript/blob/83feda2af955df1ef9f3a8080338f506f0fdf696/CONTRIBUTING.md) resource. There is _not yet_ any canonical data at moment of creating this issue. You may come up with test cases yourself or (recommended) check tracks that have already implemented this exercise for inspiration.