编写函数，以一颗树的根为输入，返回一颗对应的二叉树，给出c++代码

以下是一个示例代码，树的节点结构体定义为Node，二叉树的节点结构体定义为BinaryNode：

typedef struct Node {
    int val;
    Node* left;
    Node* right;
    Node* next;
} Node;

typedef struct BinaryNode {
    int val;
    BinaryNode* left;
    BinaryNode* right;
} BinaryNode;

BinaryNode* constructBinaryTree(Node* root) {
    if (root == NULL) {
        return NULL;
    }
    BinaryNode* binaryRoot = (BinaryNode*)malloc(sizeof(BinaryNode));
    binaryRoot->val = root->val;
    binaryRoot->left = NULL;
    binaryRoot->right = NULL;
    Node* curr = root;
    while (curr != NULL) {
        BinaryNode* binaryCurr = binaryRoot;
        while (binaryCurr != NULL) {
            if (curr->left != NULL) {
                binaryCurr->left = (BinaryNode*)malloc(sizeof(BinaryNode));
                binaryCurr->left->val = curr->left->val;
                binaryCurr->left->left = NULL;
                binaryCurr->left->right = NULL;
            }
            if (curr->right != NULL) {
                binaryCurr->right = (BinaryNode*)malloc(sizeof(BinaryNode));
                binaryCurr->right->val = curr->right->val;
                binaryCurr->right->left = NULL;
                binaryCurr->right->right = NULL;
            }
            binaryCurr = binaryCurr->next;
            curr = curr->next;
        }
        curr = binaryCurr = binaryRoot->left;
        binaryRoot->left = binaryRoot->right = NULL;
    }
    return binaryRoot;
}

该函数的实现方式是利用树的next指针，按层遍历树，并将每个节点的左右子节点依次加入到二叉树的左右节点中。