Parse a Chinese number to an arabic number

ChineseNumber.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace ChineseNumberParser
{
    internal class ChineseNumber
    {
        private int value;
        public int Value
        {
            get
            {
                // 小于10的直接返回值
                if (Factor <= 1)
                {
                    return value;
                }
                else
                {
                    int left = (Left != null ? Left.Value : 1) * Factor;
                    int right = Right != null ? Right.Value : 0;
                    // 处理”一百七“这种缩写
                    if (Right != null && Right.Factor == 1 && Right.Left == null && this.Factor > 10)
                    {
                        right = right * (this.Factor / 10);
                    }
                    return left + right;
                }
            }
            set { this.value = value; }
        }
        public int Factor { get; private set; }
        public ChineseNumber Left { get; set; }
        public ChineseNumber Right { get; set; }
        public string Text {get;private set;}

        private ChineseNumber() { }

        public static ChineseNumber Zero    { get { return new ChineseNumber { Value = 0, Factor = 0, Text = "零" }; } }
        public static ChineseNumber One     { get { return new ChineseNumber { Value = 1, Factor = 1, Text = "一" }; } }
        public static ChineseNumber Two     { get { return new ChineseNumber { Value = 2, Factor = 1, Text = "二" }; } }
        public static ChineseNumber Three   { get { return new ChineseNumber { Value = 3, Factor = 1, Text = "三" }; } }
        public static ChineseNumber Four    { get { return new ChineseNumber { Value = 4, Factor = 1, Text = "四" }; } }
        public static ChineseNumber Five    { get { return new ChineseNumber { Value = 5, Factor = 1, Text = "五" }; } }
        public static ChineseNumber Six     { get { return new ChineseNumber { Value = 6, Factor = 1, Text = "六" }; } }
        public static ChineseNumber Seven   { get { return new ChineseNumber { Value = 7, Factor = 1, Text = "七" }; } }
        public static ChineseNumber Eight   { get { return new ChineseNumber { Value = 8, Factor = 1, Text = "八" }; } }
        public static ChineseNumber Nine    { get { return new ChineseNumber { Value = 9, Factor = 1, Text = "九" }; } }
        public static ChineseNumber Ten             { get { return new ChineseNumber { Factor = 10, Text = "十" }; } }
        public static ChineseNumber Hundred         { get { return new ChineseNumber { Factor = 100, Text = "百" }; } }
        public static ChineseNumber Thousand        { get { return new ChineseNumber { Factor = 1000, Text = "千" }; } }
        public static ChineseNumber TenThousand     { get { return new ChineseNumber { Factor = 10000, Text = "万" }; } }
        public static ChineseNumber HundredMillion  { get { return new ChineseNumber { Factor = 100000000, Text = "亿" }; } }

        public static ChineseNumber Parse(char number)
        {
            return Parse(number.ToString());
        }
        public static ChineseNumber Parse(string number)
        { 
            switch (number)
            {
                case "零" : return Zero;
                case "一" : return One;
                case "二" : return Two;
                case "三" : return Three;
                case "四" : return Four;
                case "五" : return Five;
                case "六" : return Six;
                case "七" : return Seven;
                case "八" : return Eight;
                case "九" : return Nine;
                case "十" : return Ten;
                case "百" : return Hundred;
                case "千" : return Thousand;
                case "万" : return TenThousand;
                case "亿" : return HundredMillion;
                default: throw new ArgumentException("not a chinese number");
            }
        }

        public override string ToString()
        {
            return Value.ToString();
        }
    }
}

Parser.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace ChineseNumberParser
{
    public static class Parser
    {
        public static int ToArabicNumber(this string chineseNumber)
        {
            if (string.IsNullOrEmpty(chineseNumber))
                throw new ArgumentException("not a chinese number");
            ChineseNumber root = null;
            foreach (var arbic in chineseNumber)
            {
                var current = ChineseNumber.Parse(arbic);
                if (root == null)
                {
                    root = current;
                }
                else
                {
                    if (current.Factor == root.Factor)
                        throw new ArgumentException("not a chinese number");
                    root = BuildChineseNumberTree(root, current);
                }
            }
            return root.Value;
        }

        private static ChineseNumber BuildChineseNumberTree(ChineseNumber root, ChineseNumber current)
        {
            if (current.Factor > root.Factor)
            {
                current.Left = root;
                return current;
            }
            else
            {
                if (root.Right == null)
                {
                    root.Right = current;
                    return root;
                }
                else
                {
                    root.Right = BuildChineseNumberTree(root.Right, current);
                    return root;
                }
            }
        }
    }
}

ParserTest.cs

public void ToArbicNumberTest()
{
    Assert.AreEqual(25, "二十五".ToArabicNumber());
    Assert.AreEqual(107, "一百零七".ToArabicNumber());
    Assert.AreEqual(170, "一百七十".ToArabicNumber());
    Assert.AreEqual(513, "五百一十三".ToArabicNumber());
    Assert.AreEqual(365894, "三十六万五千八百九十四".ToArabicNumber());
    Assert.AreEqual(670000000, "六亿七千万".ToArabicNumber());
    Assert.AreEqual(100700000, "一亿零七十万".ToArabicNumber());
    Assert.AreEqual(100700000, "一亿七十万".ToArabicNumber());
    Assert.AreEqual(170000000, "一亿七".ToArabicNumber());
}