Uncaught TypeError: questionlist.add is not a function

var score=0;
var footer=document.getElementById('progress');
var questionDiv=document.getElementById('question');
var choiceButton1=document.getElementById('choice0');
var choiceButton2=document.getElementById('choice1');
var questionButton=document.getElementsByClassName('btn--default');


function Question(question, answer, wrongAnswer){
  this.question=question;
  this.answer=answer;
  this.wrongAnswer=wrongAnswer;
};

function Quiz(){
  this.questionList=[];
  this.questionIndex=0;

};

var questionlist= new Quiz();


var q1=new Question('What is the name of the first president ?', 'George Washington', 'Benjamin Franklin');

var q2=new Question('What is the ships name on Star Trek?', 'Enterprise', 'Applepise');


 questionlist.add(q1);
 questionlist.add(q2);