We consider general atom-bond sum-connectivity indices \(\mathcal {ABS}_{\ell }\) for \(1/2 \le \ell \le 1\) and study their values over all trees on a given number of vertices with a fixed maximum degree \(\Delta \) . We obtain both the minimum and the maximum values and characterize the corresponding trees. The obtained results recover previously known results for the atom-bond sum-connectivity index and imply analogous results for the well-known harmonic index. The results remain valid when the class of considered graphs is restricted to the class of molecular trees.
