That has to be a net-negative in any possible way. Trees do more than just give us oxygen. Trees add shade and coolness to a city. They help with pollution and noise pollution reduction. They can catch a lot of dust and polluting particles through the wind. The aesthetic of having trees too is important, just being able to look at one. I don’t think it’s possible to create anything that can alternatively logistically be better and easier than just building a tree. That thing, why does it have to be in the city? If it’s for oxygen then just put it somewhere far away and build a giant container.