Q.weeping willow tree
my tree has leaves on top but not on bottom what could be the problem

I would do a careful examine of the tree. Check the trunk, bark, leaves and branches for signs of disease or pests.
Have you had drought or excess rain?
Did the tree drop leaves or never grow them out in the spring?
These links may help you access the tree.
https://www.gardeningknowhow.com/ornamental/trees/willow/treat-peeling-willow-bark.htm
https://www.gardeningknowhow.com/ornamental/trees/willow/willow-scab-disease.htm
https://www.gardeningknowhow.com/ornamental/trees/willow/planting-weeping-willow-trees.htm