The Judas Tree is a type of redbud (fabaceae) called Cercis siliquastrum which is native to southwest Europe and southwest Asia. They average 20-30 feet and rarely grow to be taller than 50 feet, and even their typical heights are rare for a redbud.

These trees were originally from the Mediterranean and their name means, "Tree Cultivated in Jerusalem". The leaves are a lime green and heart shaped and the flowers usually are dark rose and resemble pea flowers. Various relatives have colors from dark red to white. It is considered to be a legume, provides nectar for bees, produces brown seed pods which are eaten by birds, and has yellow-green leaves in the fall. Sun or partial shade is the best place for these trees to grow, in moderate or rich soil which is well drained.

"Judas Tree" came from the story of Judas Iscariot, the betrayer of Christ. It is said when he hung himself on one of these trees, the flowers turned from white to red because of his blood and the tree's shame.

Sources:
http://www.parks.ci.portland.or.us/urbanforestry/trees/CESI.html
http://www.pynchon.pomona.edu/v/judastree.html
http://www.ces.ncsu.edu/depts/hort/consumer/factsheets/native/cercis_canadensis.html