The sorting problem: trivial trees

Like trivial lists, trivial trees are often rewritten

int tt_insert(struct node *tree, char *s)
{
    struct node *new, **nextp;
    if (strcmp(tree->s, s) > 0) {
        if (tree->left)
            return tt_insert(tree->left, s);
        else
            nextp = &tree->left;
    } else {
        if (tree->right)
            return tt_insert(tree->right, s);
        else
            nextp = &tree->right;
    }
    new = calloc(1, sizeof(*new));
    if (!new)
        return -1;
    strcpy(new->s, s);
    *nextp = new;
    return 0;
}

struct node {
    char s[SLEN];
    struct node *left;
    struct node *right;
};