how can we add an element in the map of set...eg .map

i want add an element to the mp[x]. map<int,unordered_multiset>adj;

for(int i=0;i<n;i++)
{
    cin>>brr[i];
    if(brr[i]!=arr[i])
    {
    // i want to add an element 
    //in mp[brr[i]] ;
     
    }
    else
    {
        comp.insert({brr[i],i+1}); //set
    }
}
}