I am not an expert (even an armchair expert), but I have to imagine it couldn't be that simple. When the trees die, they need to either be replaced, or self-replace. That means the land they are planted on needs to be protected. Further, when the trees die, they will release a portion of the sequestered CO2 back into the atmosphere. I wonder what percentage is re-released? Does this imply that we need an ever-growing number of trees to offset steady-state carbon emissions?
I think the tree survival rate is baked into the numbers, and most of these trees will outlive me anyway, so year-over-year CO2 I think would be fine. The EOL question is discussed in sibling comments and seems to be the crux of the issue. It seems like it mostly hinges on whether permanently increase the % of land that's covered by forest, or whether it reverts to something else once the trees die.
Based on wikipedia ([1], [2]), worldwide tree density is about 750 trees/hectare, with 4B hectares total (30% of land area). We clearly can't add another 7B to offset global emissions, but seems like a good marginal investment as long as there's room to grow that number. [3]
The real question is whether that $1 is enough to permanently "create more forest" Even at 5x the price it seems like a bargain for a lifetime of carbon emissions.
Even at $1/per tree, that is still extremely expensive when you consider that developing countries will need trees to offset their emissions as well. As an American ~$600-$3000 isn't a huge deal, but that outstrips the gdp per capita of many countries.
We should plant lots of trees, but we should also do everything else in our power in parallel.
[1] https://www.nationalforests.org/get-involved/tree-planting-p...