As a Pagan, this was probably the first time I really sat and paid attention to the seasons as they were changing. Of course I'd noticed the seasons before, but usually it was only when they did something to really catch my attention-- the first day in late fall that you needed to fish out that heavy coat, or the first day you realize you can shed your jacket because it's getting too hot. That night in winter where you realize it's dark already when you're coming home, or that summer night when you can't believe it's 8:00 and still light out.
By observing the tree a couple of times per week it made me sit up and take notice of more gradual changes that go on. and helped me attune to those.
My Tip for You Today:
Get out and pick a tree of your own to observe. You don't have to sketch it, but feel free to do so, or to take pictures of it. Just start watching it daily, weekly, noting all the minor changes going on with the tree, as well as the changes around it-- the air, the light, etc.; this can be a great minor daily meditation if you have a tree right outside your door or near where you work.