All my life I've lived in the Pacific Northwest, where fresh Christmas trees are in abundance. There is no shortage of places to buy one. We used to buy one from a lot, but lately we've been going to a farm, hiking into the woods, and choosing and cutting our own tree (a lot of fun!).
I have to say that in all the years I've lived here, growing up and then on my own, I have never once tipped a Christmas tree stand/farm worker. I don't know anybody who does that. It would absolutely never in a million years cross my mind to do so.
Tipping ... where does/will it end? Can't somebody just do their job without expecting the customer to give them money? Can't I simply buy something? IMO, when I buy a Christmas tree from a lot of wherever, part of what I am paying for is the strong young man who may or may not help me get the tree to my car. For heaven's sake, they don't even net it for free anymore - that costs extra.
So, no. I do not and will not tip for being allowed to buy a Christmas tree. Sorry.