push_back() binary tree into vector

I'm trying to put all the elements from a binary search tree into a vector, in order. Here is the function:

    void inOrder(std::vector <double> & v) {
    TreeNode **tree = &root;

    while (tree) {
        std::cout << "Arranging in order." << std::endl;
        if ((*tree)->value) {
            tree = &(*tree)->left;
            std::cout << tree << std::endl;
            v.push_back((*tree)->value);
        }
        else {
            tree = &(*tree)->right;
            std::cout << tree << std::endl;
            v.push_back((*tree)->value);
        }
    }

}
};

I'm unable to get the values to push into the vector. Any ideas as to how I can accomplish this?