![image](https://user-images.githubusercontent.com/6652840/126856263-58f9c1bc-29c5-4a45-8acc-12af65203f60.png)
This happened with Firefox 89 on Linux. It also happened with Chromium 91, also on Linux.
Note that the "declare premises" button fixes this issue: this only happens when createTree is called with a tree with long parts and "declare premises" is not pressed again.
This came from this exercise I grabbed from the forallx-UBC textbook while writing docs: