A new scheme for deploying multicasting in MPLS networks is proposed. Each possible tree in an MPLS network is assigned a number, which is then used to classify the corresponding multicast session into its FEC. We call this approach Tree Numbering (TN). It provides the capability to aggregate different multicast flows (sessions) having the same tree "shape". The assigned number is calculated distributedly by adding the partial weight values generated by the LSRs and the ingress LER of the corresponding tree. The key point in our approach is that the assigned numbers needed to distinguish the "shapes" of all the possible trees depend on the number of possible egress LERs could be reached by that ingress LERs and not on the number of the LSRs (core routers). In terms of the memory size, the proposed approach outperforms the approach that stores the IP addresses of the multicast tree or the one that store the concatenation of the sub codes generated by the ingress LER and the LSRs.