GEMARA: With regard to laborers, the Sages taught in a Tosefta: Laborers, while engaged in their labor, may recite Shema while standing atop the tree or atop the course of stones in a wall under construction. And they may pray atop the olive tree or the fig tree, as those trees have many branches close together, so one could stand on them and focus properly while praying. In the case of all the rest of the trees, however, they must climb down and pray. However, the homeowner, who is self-employed, in all cases, regardless of the type of tree, must climb down and pray, as he will be unable to focus appropriately. Since, in contrast to the laborers, it is his prerogative to climb down and pray, the Sages did not permit him to pray atop the tree.