  We develop basic cluster theory from an elementary point of view using a
variation of binary trees which we call mixed cobinary trees. We show that the
number of isomorphism classes of such trees is given by the Catalan number Cn
where n is the number of internal nodes. We also consider the corresponding
quiver Q_{\epsilon} of type An-1. As a special case of more general known
results about the relation between c-vectors, representations of quivers and
their semi-invariants, we explain the bijection between mixed cobinary trees
and the vertices of the generalized associahedron corresponding to the quiver
Q_{\epsilon}.
