1. A non-transitory computer-readable medium having computer-executable instructions for causing a computer system to perform a method for improving parallelism while determining a plurality of bounding volumes in a binary tree in a parallel fashion using a strict depth-first order by processing each node by one thread when employing at least a first thread and a second thread, said method comprising: providing said binary tree comprising a plurality of leaf nodes and a plurality of internal nodes, wherein each of said plurality of internal nodes is uniquely associated with two child nodes each comprising either an internal node or leaf node; and determining said plurality of bounding volumes for nodes in said binary tree by traversing said binary tree from said plurality of leaf nodes upwards toward a root node, wherein a plurality of paths from said plurality of leaf nodes to said root node are processed in parallel, and wherein each parent node is processed once by a later arriving corresponding child node, wherein said determining said plurality of bounding volumes comprises: atomically traversing to a first parent node from a first child node on said first thread, wherein said first parent node is associated with said first child node and a second child node; determining whether said first parent node as been traversed to before by said second child node on said second thread; terminating traversal to said first parent node on said first thread when said first parent node has not been traversed to before by said second child node; and selecting an unprocessed leaf node; and traversing said binary tree beginning from said unprocessed leaf node that is selected.