appendChild() is not a function appears even though it´s used for an ul element

Question

I´m trying to create a to-do list and struggling with adding entries to the list. I always get the error "list.appendChild is not a function" when clicking on my button even though my list is a DOM element (ul).

function Add(){
    var list = document.getElementsByTagName("ul");
    var li = document.createElement("li");
    var input = document.getElementById("input").value;
    var content = document.createTextNode(input);
    li.appendChild(content);
    list.appendChild(li);
}

Help would be greatly appreciated