Mysterious appearance of a pine tree

[Miretar]

there is one pine tree growing on my farm to produce pine resin. All the others have been chopped down. I have twice had pine trees spawn; the second time on the other other side of the farm. most of the spaces in between are covered with grass, with the exception of places where I needed to remove weeds.

Where are these trees coming from?

 

[imnvs]

Trees will randomly spawn on your farm starting as a seed, just like weeds, twigs and rocks. The way I look at it, they're coming from the trees you can see surrounding your farm that you don't have access too.