In multicast communication, a single source transmits the same content to a large amount of receivers. This kind of communication is usually represented following a tree model where the root of the tree is the multicast source and the leaves are the receivers. Scalability problems arise when the root needs to collect data (sensor information, metering data, etc.) from the leaves. This results in a many-to-one (leaf-to-root) communication. The matter is further complicated if there are security requirements on the leaf-to-root traffic.