The Trillion Tree project started originally as a Billion Tree project.

Read Wikipedia for the history: https://en.wikipedia.org/wiki/Trillion_Tree_Campaign

It was formally launched at the Davos World Economic Forum in 2020:
https://www.weforum.org/agenda/2020/01/one-trillion-trees-world-economic-forum-launches-plan-to-help-nature-and-the-climate/

Time Magazine wrote in August 2021:
Yes, We Can Grow 1 Trillion Trees to Help Fight Climate Change

Planting one trillion trees won’t be easy. It will depend on all of us taking action in our countries, our companies and our communities.