Zone 7. What is this decorative tree in a park?
It's a Redbud. If you're in the US, that could be Cercis canadensis (Eastern Redbud), Cercis chinensis (Chinese Redbud), or two sub-species of Cercis canadensis, the Mexican and Oklahoma Redbuds. The Chinese Redbud is the smallest of these trees, with the others are approximately 20-25 feet tall and 20 feet wide. They're not a particularly fast-growing tree, but very pretty when in bloom in spring. The Eastern Redbud also has nice (yellow) fall color.