Answer: I think the perfect tree for you is the Snow Fountain Weeping Cherry Tree. It has a cascading habit and compact growth habit. This slow-growing dwarf has graceful branches that bend to the ground and each spring the Snow Fountain Weeping Cherry Tree dons a floral cloak of pure white so beautiful it rivals any flowering ornamental. Ultimately reaches a height of 12-15' and spreads 6-8'. Very hardy, disease and insect resistant. Because it remains small, the root system should not cause problems in the restricted space you describe, but there's always the possibility of planting it in a large container rather than directly in the ground. This way you can keep the roots restricted and give your tree some decent soil in which to grow.
Best wishes with your new tree!
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