I got a strange bug when playing it again if the tree is fertillized too much. The tree vanishes, and it starts alternating between huge negative and positive numbers . It's possible to wait for it to turn positive from time to time, and buy tons of stuff.
Viewing post in Petville (Brackeys Game jam 2024) jam comments
I played it again, I really like this game. I checked where I think is the max level the tree should be and not to upgrade past this point for now in case I want to avoid getting this issue.
This is the number with no pets, if there's some pets it would show as a bit higher, but it's something like 146 or higher and the tree looks like this when it should stop being upgraded to avoid the issue for now: