// (WRONG)
int x = v[i]; // the new v[i], that is
v.erase(v.begin() + i);
v.insert(
    std::upper_bound(v.begin() + i, v.end(), x),
    x
)

int x = v[i]; // the new v[i], that is
if (/* new v[i] is > old v[i] */) {
    size_t j = i + 1;
    while (v[j] < x && j < v.size()) {
        std::swap(v[j-1], v[j])
        j++;
    }
}