We've had some previous discussions in these forums about scouts collecting old christmas trees for use in conservation projects like beach dune replenishment or soil erosion control in woodlands or stream beds. But these discussions were mostly about doing it for the conservation impact, not necessarily to raise funds.
Yet a well-planned conservation project often CAN be a very effective fund raiser.
There's a new article in the Bryan on Scouting blog that shows how one troop made this work: https://blog.scoutingmagazine.org/2020/01/29/oh-christmas-tree-troops-unique-project-blends