  We study the supersymmetric ground states of the Kronecker model of quiver
quantum mechanics. This is the simplest quiver with two gauge groups and
bifundamental matter fields, and appears universally in four-dimensional N=2
systems. The ground state degeneracy may be written as a multi-dimensional
contour integral, and the enumeration of poles can be simply phrased as
counting bipartite trees. We solve this combinatorics problem, thereby
obtaining exact formulas for the degeneracies of an infinite class of models.
We also develop an algorithm to compute the angular momentum of the ground
states, and present explicit expressions for the refined indices of theories
where one rank is small.
