public CallTree align() {
        // populate call tree
        populate();
        // link to span
        link();
        // fill missing span
        fill();
        // remove unlinked
        clear();
        // select root
        final CallTree callTree = root();
        // pruning non productive node
        callTree.pruning(callTreeNodeNonProductiveFilter);

        return callTree;
    }
@author netspider
@author emeroad
@author jaehong.kim
web/src/main/java/com/navercorp/pinpoint/web/calltree/span/SpanAligner.java