We study the spectrum of Laplacian for trees, and make an approach to ordering trees by the spectral radius of Laplacian. A general method of ordering trees is derived as well, and as its applications, we give the optimal estimates of the orderings of two types of trees.
Jinsong Tan. "Ordering trees by the spectral radius of Laplacian." Proc. Japan Acad. Ser. A Math. Sci. 75 (10) 188 - 193, Dec. 1999. https://doi.org/10.3792/pjaa.75.188