Yes, although on this map I think the trees in parks are not shown
It's based on data from councils and tfl, so council run parks are included (e.g. Gunnersbury near where I live) but not royal parks (like Richmond park)
Seems there are at least a few trees missing in some of the council parks near me, but most of them are there. Quite nice.
And then there is the green belt around London. This sort of thing probably encourages building up not out which is probably a good thing.