static void insert(BinTree * node, int key) {
    if (key < node->value) {
        if (node->left == NULL) {
            node->left = BinTree_new(key);
        } else {
            insert(node->left, key);
        }
    } else if (key > node->value) {
        if (node->right == NULL) {
            node->right = BinTree_new(key);
        } else {
            insert(node->right, key);
        }
    } else {
        assert(0 && "Dublicate key");
        fprintf(stderr, "Dublicate key");
        abort();
    }

}

void BSTree_insert(BSTree * self, int key) {
    if (self->root == NULL) {
        self->root = BinTree_new(key);
    } else {
        insert(self->root, key);
    }
}