In one of Katsushika Hokusai's prints, three men are seen working with ropes in a tree against the backdrop of Mount Fuji. On the evidence of their clothing, they belong to the Sora-Shi ethnic group, 空師, which literally means “people of heaven.” This is the group from which the shoguns, the leaders of the samurai, recruited their ninjas.
When the old power structures changed at the end of the 18th century and the services of the ninjas were no longer in such demand, they had to look for new fields of activity. So they started doing rope work at height, such as on rocks or trees.
So people who work in trees are a little bit ninja - just in high-viz vests.