Wavelength-division multiplexed (WDM) networks using wavelength-routing are considered to be potential candidates for the next generation wide-area backbone networks. This paper concerns with the problem of multicast routing in WDM networks. A node in the network may have both wavelength conversion and splitting capabilities which is called as virtual source. It is assumed that virtual sources are limited in number and are distributed evenly in the network. This paper proposes a new approach, which makes use of these special capable virtual sources to construct a multicast tree.