A subtree refers to a node, all its children, all of the children's children, etc. A subtree is like a little tree linked onto a larger tree (although the entire tree is also a subtree). Calling this function for a node outputs the subtree to the file described by the iostream variable outputFile. Usually users will invoke this routine through the top-level node to output the whole tree. This routine outputs each node in the tree individually by calling the member function IOData(), which is different for each node type.
eventNode *ev; fstream outfile; ... ev->outputSubtree(outfile);