From the Dictionary of American Family Names, Oxford University Press, ISBN 0-19-508137-4, from the Ancestry.com website:
Treat is an Americanized spelling of German Tritt.

Tritt is German: apparently from Old High German tretan ‘to step’. However, a South German family of that name are the descendants of late 16th-century immigrants from Como, Italy who bore the name de Triddi.

My Treat ancestors are primarily in Eastern Arkansas in the early 1900s and late 1800s.  One of the most interest Treat ancestors is Steven Treat

Stephen was a legendary father, husband, pioneer, founder, mason, boxer, strongman, hunter, and “Minister of the Gospel”.