Pass

**Very well done Felix!**

Yeah, your are right. Your tree is not only slow, but lack functions such as `size`. These tests are also interestingly named:
```rs
#[test]
fn tree_is_balanced() {
//...
assert_eq!(b, 0);
}

#[test]
fn tree_is_really_balanced() {
//...
assert_eq!(b, 0);
}
```
I would have liked you to instead have one test for `assert_eq!(b, 0)` and one for `assert_eq!(b, 1)`.

_Sad spagetti_:
```rs
// get input lines as iterative
//let lines: Vec = input
// .lock()
// .lines()
// .map(|_line| _line.ok().unwrap())
// .collect();
```

The issue contains review comments about tree performance, a missing size function, test naming, balance assertions, and commented iterative input code, but names no files or acceptance criteria. Start by locating the tree implementation and its balance tests; no clear definition of done is provided.

Written by the indexing model from the issue text.