huffman编码问题

//我是用最小堆实现的，以下是建立Huffman树的算法
struct HuffmanNode
{
    int data;
    HuffmanNode *leftChild,*rightChild;
    HuffmanNode():leftChild(NULL),rightChild(NULL){}
    HuffmanNode(int value):data(value),leftChild(NULL),rightChild(NULL){}
    bool operator<=(HuffmanNode& R){return data <= R.data;}
    bool operator>(HuffmanNode& R){return data > R.data;}
    bool operator>=(HuffmanNode& R){return data >= R.data;}
};

void mergeTree(HuffmanNode& bt1,HuffmanNode& bt2,HuffmanNode*& parent)//合并
{
    parent = new HuffmanNode;
    parent->leftChild = &bt1;
    parent->rightChild = &bt2;
    parent->data = bt1.data+bt2.data;
}

HuffmanNode*& HuffmanTree(int value[],int n)
{
    MinHeap<HuffmanNode> min_heap;
    HuffmanNode first,second,*parent;

    for(int i=0;i<n;i++){
        HuffmanNode temp = HuffmanNode(value[i]);
        min_heap.Insert(temp);
    }
    for(int i=0;i<n-1;i++){
        min_heap.Remove(first);
        min_heap.Remove(second);
        mergeTree(first,second,parent);
        min_heap.Insert(*parent);
    }
    return parent;
}

//运行时程序出错