Looping an IF statement whilst a boolean function returns true

I'm struggling with creating a very simple loop that repeats and IF statement whilst a boolean function returns true. Here is the code:

bool agreeToContinue();
if (agreeToContinue() == true)
{               
    void drawAXmasTree();
    drawAXmasTree();        
}

All I want it to do is simply repeat the IF statement whilst the boolean function is returning true. Thanks :)