The quick but incorrect way to remedy the problem would be to eliminate the Leaf class and represent Leaf nodes simply by putting null Pointers in the left and right fields of a Branch.

One day while I was hiding behind a wall, looking out toward the fields, I felt a terrible blow to my right eye.

Later, they learned to work with the seasons, planting at the right time and, in dry areas, making use of annual floods to irrigate their fields.