Using MatterJS I have a stack of circles and a floor rectangle:

var stack = Composites.stack(300, 0, 3, 3, 10, 10, function(x, y) {
    return Bodies.circle(x, y, Common.random(10, 20), {friction: 0, restitution: 0.2, density: 0.001 });
}); 

Composite.add(world, stack);

Composite.add(world, [
    Bodies.rectangle(300, 300, 600, 20, { isStatic: true, friction: 0, render: { fillStyle: '#060a19' } }),
]); 

How do I make those circles ignore each other and only collide with my floor rectangle?