Given a multicast session in Wavelength Division Multiplexing (WDM) networks, we try to find the multicast light-trees with the minimum power budget while taking into account the optical power loss as light splitting loss, node tapping loss and light attenuation loss. Although light splitting causes non-linear power relationship, we succeed to formulate this problem as a Mixed-Integer Linear Programming (MILP) by developing a set of equivalent linear equations to replace the non-linear ones. The distribution of power loss is analyzed by simulations, which suggests to bound the combined power loss ratio of the node tapping loss and the light attenuation in each source-destination path, and make power-symmetric light-trees by properly using light-splitters in order to minimize the overall power loss.