public void goLeft() {
	if(!currentNode.isEmpty()) {
		stack.push(currentNode);
		currentNode = currentNode.left;
	}
}

public void goUp() {
	if(!stack.isEmpty()) {
		currentNode = stack.peek();
		stack.pop();
	}
}

public void goRoot() {
	do {
		currentNode = stack.peek();
		stack.pop();
	} while(!stack.isEmpty());
}