code: public CallTreeNode onStopwatchStop(Split split) {
  		CallTreeNode currentNode = callStack.removeLast();
  		currentNode.addSplit(split);
  		if (callStack.isEmpty()) {
  			onRootStopwatchStop(currentNode, split);
  		}
  		return currentNode;
  	}
docs: When stopwatch is stopped, the the split is added to current tree node
  and this tree node is popped from call stack.
  As a result, parent tree node becomes current tree node.
  
  @return Current (child) tree node