There’s a simple beauty to the March Madness bracket.

A tree diagram that starts with 68 horizontal lines on its fringes whittles itself down via perpendicular vertical lines until only one horizontal line remains at its center.

That basic geometry has become the symbol for a cultural phenomenon that enchants the nation for one month each year and entices millions of Americans to participate — turning the month of March into big business for men’s and women’s college basketball.

The biggest draw? The storylines behind scrappy underdogs: The unexpected come-ups of a Saint Peter’s, or a George Mason, or a Fairleigh Dickinson can only exist in the format.