The tree, in my view reffers to the actions you perform while when you make a kind gesture, or when, in a state of awareness you decide to take a decision which some time later on, will bring you some results. Is like when you decide to study hard for an exam: you are planting the tree (taking the right actions) to enjoy its benefits (such as shade, birds nearby, fruits, was etc) , but in this case to pass the exam which will be a step further in your career. Hope this helps :)