我的程序出错，请教高手指点。小弟不胜感激！

public class HuffmanTree
{
    private Node[] data;    // 结点数组
    private int leafNum;    // 叶子结点数目
 
    // 索引器
    public Node this[int index]
    {

        get
         {
             return data[index];
}
set
{
    data[index] = value;
}
}
 
// 叶子结点数目属性
public int LeafNum
    {
        get
         {
             return leafNum;
}
set
{
    leafNum = value;
}
}
 
// 构造器
public HuffmanTree (int n)
{
   Node[]  data = new Node[2*n-1];
leafNum = n;
}
 
// 创建哈夫曼树
public void Create()
{
   
 
    // 输入n 个叶子结点的权值
            for (int i = 0; i < leafNum; ++i)
            {
                data[i].Weight = Convert.ToInt32( Console.ReadLine());
             }
 

    //处理 n 个叶子结点，建立哈夫曼树
            for (int i = 0; i < this.leafNum - 1; ++i)
            {
               
               
                int max2;
                int tmp2;
                int max1 = Int32.MaxValue;
                max2 = Int32.MaxValue;
               int tmp1 = tmp2 = 0;
 
                //在全部结点中找权值最小的两个结点
                for (int j = 0; j < this.leafNum + i; ++j)
                {
                    if ((data[i].Weight < max1)  
&& (data[i].Parent == -1))
                    {
                        max2 = max1;
                        tmp2 = tmp1;
                        tmp1 = j;
                        max1 = data[j].Weight;
                    }
                    else if ((data[i].Weight < max2)  
&& (data[i].Parent == -1))
                    {
                        max2 = data[j].Weight;
                        tmp2 = j;
                    }
                }
 
                data[tmp1].Parent = this.leafNum + i;
                data[this.leafNum + i].Weight = data[tmp1].Weight  
+ data[tmp2].Weight;
                data[this.leafNum + i].LChild = tmp1;
                data[this.leafNum + i].RChild = tmp2;
    }
}
}


    class Program
    {
        static void Main(string[] args)
        {
            HuffmanTree ht = new HuffmanTree(21);
            ht.Create();
        }
    }
}

不好意思，Node是个类，在程序里已经定义 就是忘了把代码贴出来了。