The amount of effort required for 10 million trees a day would require everyone in the US to plant a tree each month. This would likely also require people to care for enough saplings to plant a new tree each month.
It's not an insurmountable level of effort per person, but if you try to do it on a large scale you inevitably end up with logistical problems, and it would require quite a lot of space.
I am not sure I understand your math here. Let’s say every adult in the US, 300M, plants a tree each month for 12 months, 3.6B trees planted in a year. Or are you factoring in saplings that fail to grow or something? Is it that bad that for every 160 trees planted only one survives?
Edit: strike that I see what you meant there with the a day. I just should have actually read what you wrote before I commented.
I did some quick googling and the first figure I found was that Americans plant around 1.6 billion trees every year. That is around 4.4 million every day, almost half of what is required for the carbon offset claims by GP.
Actually 20 million trees every 2 days doesn’t sound that ridiculous. Especially as we build more green infrastructure and reduce the daily emissions.
It's not an insurmountable level of effort per person, but if you try to do it on a large scale you inevitably end up with logistical problems, and it would require quite a lot of space.