To insert an element into an std::unordered_set container in C++, you can use the insert() method. Here are a few examples:

#include <iostream>
#include <unordered_set>

int main() {
    std::unordered_set<int> mySet = {1, 2, 3};

    // Insert a single element
    mySet.insert(4);

    // Insert multiple elements using an initializer list
    mySet.insert({5, 6, 7});

    // Insert elements using a range of iterators
    std::vector<int> vec = {8, 9, 10};
    mySet.insert(vec.begin(), vec.end());

    // Print the contents of the set
    for (const auto& elem : mySet) {
        std::cout << elem << " ";
    }
    std::cout << std::endl;

    return 0;
}

This program creates an std::unordered_set container called mySet with the values 1, 2, and 3. It then demonstrates how to insert elements into the set using various methods. Finally, it prints the contents of the set to the console. The output of this program will be:

1 2 3 4 5 6 7 8 9 10

Note that since the elements of an unordered set are not stored in any particular order, the elements will not necessarily be printed in the same order as they were inserted.