public String toTreeStr() {
		if (left == null && right == null)
			return (value == null ? "" : value.toString());

		String result = (value == null ? "" : value.toString()) + "(";
		if (left != null) {
			result += left.toTreeStr();
		}
		result += ",";
		if (right != null) {
			result += right.toTreeStr();
		}
		result += ")";
		return result;
	}