how to find the subsequences of an array

vector<vector<int>> subsequences(vector<int> arr, int index){
    if(index == 0){
        return {{}, {arr[0]}};
    }
    vector<vector<int>> smallAns = subsequences(arr, index - 1);
    int n = smallAns.size();
    for(int i = 0; i < n; i++){
        vector<int> v = smallAns[i];
        v.push_back(arr[index]);
        smallAns.push_back(v);
    }
    return smallAns;
}