Binary Search Tree: Test root node with value == 0 is allowed about c HOT 2 OPEN

static void _insert_node(node_t* tree, int value)
{
    if (!tree->data) {
        tree->data = value;

        return;
    }

    if (value <= tree->data) {
        if (!tree->left) {
            tree->left = calloc(1, sizeof(node_t));
            tree->left->data = value;
        } else {
            _insert_node(tree->left, value);
        }
    } else {
        if (!tree->right) {
            tree->right = calloc(1, sizeof(node_t));
            tree->right->data = value;
        } else {
            _insert_node(tree->right, value);
        }
    }
}

node_t *build_tree(int *tree_data, size_t tree_data_len)
{
    node_t* tree = calloc(1, sizeof(node_t));

    for (size_t i = 0; i < tree_data_len; i++) {
        _insert_node(tree, tree_data[i]);
    }

    return tree;
}