I have 2 tree peonies, one very old one that came with our house and a new one I puchased 2 years ago. The older one flowers a dark burgundy, the new one is bubblegum pink. You usually don't see blooms the first year. It takes time to establish, so the first or second spring after planting you may only have a green plant.
One reason you may not have noticed tree peonies is that they bloom once a season for a very short time in May, the rest of the year they look like a green plant or bush depending on the size. It naturally grow in a round shape, so no trimming is needed. The leaves are a different shape than peony plants.
They are low maintenance and so beautiful when they are in bloom. My neighbor has one that is about 40" high and wide, it had at least 50 huge blooms this year. Amazing!