This paper studies all-optical multicast routing in wavelength-routed optical networks with sparse light splitting. In a sparse splitting network, only a small percentage of nodes are capable of light splitting, i.e., multicast capable. The typical solutions of existing multicast routing algorithms for sparse splitting networks combine an existing Steiner Tree heuristic with some rerouting procedures to refine the trees. The resulting tree cost in terms of the total number of wavelengths used on all tree links is then very expensive. In this paper, we propose a new mechanism that constructs all-optical multicast trees for sparse splitting networks without an additional rerouting procedure in the tree construction. Two efficient approaches are suggested and evaluated by simulations. The results show that our mechanism builds light-trees with the least wavelength channel cost and with the smallest number of wavelengths used per link.