Let n and d be two positive integers. By Bn,d we denote the graph obtained by identifying an endvertex of path Pd with the center of star Sn-d+1, where n ≥ d + 1. By Cn,d we denote the graph obtained by identifying an endvertex of Pd-1 with the center of Stare Sn-d, and the other endvertex of Pd-1 with the center of S3 where n ≥ d + 3. By En,d,k we denote the graph obtained by identifying the vertex vk of P(v1 - v2 - ··· - vd+1) with the center of Sn-d. In this paper, we completely characterize all trees T which have diameter at least d(d ≥ 3) and satisfy the following conditions:(i) Z(Bn,d) ≤ Z(T) ≤Z(En,d,3) for n = d + 3; (ii) Z(Bn,d) ≤ Z(T) ≤ Z(Cn,d) for n ≥ d + 4.