Q.Redbud tree
The tree had beautiful flowers in early spring but the leaves never appeared. I was still watering the tree but no leaves. The tree is now dead….what did I do wrong?

Check the bark of the young tree, by doing the scratch test.
The link below will help you.
The flower buds on the Redbud Tree would have formed last year, so it had the energy to bloom this spring.
If you still see signs of life in the scratch test and if branches are still pliable, I would give the tree more time and even into next season to see if it has any life.
Improper planting, poor drainage, winter cold, disease or pests could all be reasons for tree loss. Sometimes you lose a tree for unknown causes.
Here are some links with more information.
https://www.gardeningknowhow.com/ornamental/trees/redbud/caring-for-redbud-trees.htm
https://www.gardeningknowhow.com/ornamental/trees/tgen/tree-scratch-test.htm
https://www.gardeningknowhow.com/ornamental/trees/tgen/tree-leafing-problems.htm