Berlin has 431k street trees. Toronto has 11 million trees (including presumably ravines and natural areas) - and I'm sure other cities have similar amounts. Why do you think Berlin has the most trees?
In German cities in my experience treets often seem more imposing or covering more space, maybe that's the difference as North American streets are much wider.
I think I may be wrong about Berlin. Googling around it does seem like Toronto and Johannesburg are close together (both around 10 million trees), but are the trees in Toronto planted or natural? In JHB most of the trees were planted.
https://i.pinimg.com/originals/7e/5e/70/7e5e7045c4443f645731...
when I think of Toronto I think more of this:
https://imgur.com/xB702UU
In German cities in my experience treets often seem more imposing or covering more space, maybe that's the difference as North American streets are much wider.