Skew Diagrams and Ordered Trees. - Robert G. Rieper; Melkamu Zeleke (Adv. Appl. Math., 2001)

On Generalizing Motzkin Numbers using k-Trees. - Mahendra Jani; Melkamu Zeleke (Ars Comb., 2008)

On Subsets of Ordered Trees Enumerated by a Subsequence of Fibonacci Numbers. - Melkamu Zeleke; Mahendra Jani (Integers, 2015)