Let G be a simple (nondirected) graph with degree sequence d1, d2,..., dn. The number of spanning trees of G is bounded above by ( n n-1)n-1 Πdi ∑di. © 1988.
Grone, R., & Merris, R. (1988). A bound for the complexity of a simple graph. Discrete Mathematics, 69(1), 97–99. https://doi.org/10.1016/0012-365X(88)90182-3