Update DistributedSystemSum.java

You are given a binary tree where each node has an integer value, a left, right and parent pointer. Every node is an independent distributed system where a thread is running in each node. You can talk to other node only by one method called "send(node, data)". And a node can call "send" only to its children or parent. How will you design the system so that all the nodes know the total sum of values of all the nodes in the binary tree and report them asynchronously.