A symbol of new life, eggs have long been traditional gifts at spring festivals, and dyed eggs have played a part in religious ceremonies since ancient times.
Why a Bunny?
An Anglo-Saxon legend tells of Eastre or Eostre, a goddess of spring, who was symbolized by the hare--a symbol of life and fertility. Another story tells of a mother who dyed Easter eggs for her children and hid the eggs in a nest. When the children found the eggs they also found a rabbit, and believed the rabbit brought the eggs.
Why a Tree?
Hanging Easter eggs from leafless branches is a European custom transplanted to the U.S. Although Easter Egg Trees were common as far back as Civil War times, they gained widespread popularity when "The Easter Egg Tree," a book by Katherine Milhous, was published in 1950.