public Node maketree() {
		Node node = null;
		if (i < tokens.size()) {
			switch (tokens.get(i)) {
			case "(":
				node = new Node(tokens.get(i));
				i++;
				node.leftNode = maketree();
				node.rightNode = maketree();
				break;

			case ")":
				i++;
				break;

			default:
				node = new Node(tokens.get(i));
				i++;
				if (i < tokens.size()) {
					if (tokens.get(i).equals("(")) {
						node.rightNode = maketree();

					} else {
						node.leftNode = maketree();
					}
					break;
				}
			}
		}
		return node;
	}