How to insert selected SVG elements in a group with javascript

I am creating some svg elements with javascript, e.g.

const svg = document.querySelector('svg');

// variable for the namespace 
const svgns = "http://www.w3.org/2000/svg"

//assigning svg element attribute 
svg.setAttribute('class', 'layer1');
svg.setAttribute('xmlns', svgns);
svg.setAttribute('width', '400');
svg.setAttribute('height', '200');
svg.setAttribute('viewBox', '0 0 400 200');

//make background
var fill1 = '#e6e6e6';
//var fill2 = 'transparent';

let bg = document.createElementNS(svgns, 'rect');
bg.setAttribute('class', 'bg');
bg.setAttribute('id', 'bg');
bg.setAttribute('width', '200');
bg.setAttribute('height', '200');
bg.setAttribute('fill', fill1);

// append the new rectangle to the svg
svg.appendChild(bg);

function createRect(a) {

    //create element
    var rect1 = document.createElementNS(svgns, 'rect');
    rect1.setAttribute('class', 'cl' + a);
    rect1.setAttribute('id', 'id' + a);
    rect1.setAttribute('x', '10');
    rect1.setAttribute('y', '20');
    rect1.setAttribute('width', '30');
    rect1.setAttribute('height', '30');
    //rect1.setAttribute("rx", "20");
    rect1.setAttribute('fill', 'red');

    svg.appendChild(rect1);
};

//create an array from  1 to 5
var bigArray = [];
for (var i = 0; i < 5; i++) {
    bigArray[i] = i + 1;
};

//create Rect for each element of the array
for (const el of bigArray) {
    createRect(el);
}

//create group
var group = document.createElementNS(svgns, 'g');
group.setAttribute('class', 'allRect');
group.setAttribute('id', 'allRect');

svg.appendChild(group);

var x = document.querySelectorAll('[class^=cl]');

<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body> 
    <svg>        
    </svg>
</body>

</html>

How can I ask javascript to insert a custom selected elements document.querySelectorAll('[class^=cl]') (all 5 Rects) in a group allRect