Although IP-multicast has been proposed and investigated for the some time, there are major problems inherent in the IP-multicasting technique, for example, scalability problems, difficulty to allocate a globally unique multicast address, complexity to support higher level features such as reliable data transfer, congestion/flow control and security, and more importantly, deployment problem due to architectural changes to core routers. Recently, End-System Multicast (ESM) has been proposed as an alternative solution so that multicasting services can be quickly deployed. In this paper, we consider the "architectural" and "optimization" issues on designing an ESM-tree. Specifically, we present a distributed algorithm on how to create and maintain an ESM-tree. We also propose a distributed algorithm to perform a tree optimization(TO) so that an ESM-tree can dynamically adapt to the changing network condition (e.g., drop in transfer bandwidth) so that nodes can receive the multicast data more efficiently. The propose distributed algorithm has the theoretical properties that at all times, a tree-topology can be maintained and that any node joining, leaving, as well as any tree optimization operation will not "partition" an ESM-tree. Therefore, our work can be used to provide an efficient architectural infrastructure for ESM services. We have implemented a prototype ESM system and carried out experiments to illustrate the effectiveness and performance of our ESM optimization protocol.