"identifier "unordered_map" is undefined" error in VS Code C++ (on Ubuntu Linux)

#include <bits/stdc++.h>

int main()
{
    std::unordered_map<int, int> test{};

    test[2] = 14;

    std::cout << test[2];
}

Errors:

• identifier "unordered_map" is undefined
• type name is not allowed
• identifier "test" is undefined

I test the code in VS Code C++ on Ubuntu Linux and I can't compile it (It works fine in an online compiler). Why do I have these errors and how to fix them?