Answer: Since rooftop conditions can be trying at best due to wind, reflected heat and limited soil space, I would suggest you experiment and see what works best. You might try the purple leafed sand cherry which has purple foliage all season long. This is technically a shrub but will grow tall enough to give the effect of a small tree. It withstands wind and temperature extremes and blooms in the spring, but does not provide edible fruit. It is usually available with stems over three feet long and grows relatively quickly.
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