I do think you mean sex, not gender - trees don't really have a gender or gender expression. Either way, it would be rather irrelevant, as most trees planted in cities have both male and female flowers (oak, birch, most conifers), or even hermaphroditic flowers (citrus).

It's not really disputed. It's something that happened in one small place or two that people insist on repeating on the internet as if it's some universal thing.