Trees are not static, unchanging, pop into existence and forget about, things. Trees that don't get regular "updates" of adequate sunlight, water, and nutrients die. In fact, too much light or water could kill it. Or soil that is not the right courseness or acidity level could hamper or prevent growth. Now add "bugs". Literal bugs, diseases, and even competing plants that could eat, poison, or choke the tree. You might be thinking of trees that are indigenous to an area. Even these compete for the resources and plagues of their area, but are more apt than the trees accustom to different environments, and even they go through the cycle of life. I think his analogy was perfect, because this is the first time coding could resemble nature. We are just used to the carefully curated human made code, as there has not been such a thing as naturally occuring, no human interaction, code before