Kousa Dogwood

Question

I planted one 6 years ago. The tree was 2 feet tall, never lost the green leaves, and never grew any higher.

Answer 1

Make sure your tree is planted in a location that gives it the conditions it needs:
https://www.gardeningknowhow.com/ornamental/trees/dogwood/growing-kousa-dogwood-trees.htm

Fertilizer can probably help with your tree's slow growth. Choose a nitrogen-rich fertilizer or organic alternative:
https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/nitrogen-plant-fertilizer.htm