How to Add more than one products of same id with different sizes in laravel session?

I am trying to add more than one product having same ID but different sizes. How can I do that. But It just override my previous product item that is added with the different size

if(!$cart) {
        $cart = [
            $request->product_id => [
                        "id"        => $request->product_id,
                        "name"      => $request->product_name,
                        "quantity"  => $request->quantity,
                        "price"     => $request->product_price,
                        "image"     => $request->product_image,
                        "costprice" => $request->product_price,
                        "color"     => $request->color,
                        "size"      => $request->size,
                    ]
        ];
        session()->put('cart', $cart);
        return redirect('/cart');

        // return redirect()->back()->with('success', 'Product added to cart successfully!');
    }
     if(isset($cart[$request->product_id]) ) {
                $cart[$request->product_id]['quantity']++;
                session()->put('cart', $cart);
                return redirect('/cart');
                
                // return redirect()->back()->with('success', 'Product added to cart successfully!');
            }

I think this code below will satisfy your requirement

if(!$cart)) {
    $cart = array(
        $request->product_id => array()
    );
   $productInfoArr=array( 
        "id"=> $request->product_id,
                         "name"      => $request->product_name,
                         "quantity"  => $request->quantity,
                         "price"     => $request->product_price,
                         "image"     => $request->product_image,
                            "costprice" => $request->product_price,
                            "color"     => $request->color,
                            "size"      => $request->size,
                     );
                
    array_push($cart[$request->product_id],$productInfoArr);
    session()->put('cart', $cart);
    return redirect('/cart');

    // return redirect()->back()->with('success', 'Product added to cart successfully!');
}

 if(isset($cart[$request->product_id])) {
            $productInfoArr=array( 
        "id"=> $request->product_id,
                         "name"      => $request->product_name,
                         "quantity"  => $request->quantity,
                         "price"     => $request->product_price,
                         "image"     => $request->product_image,
                            "costprice" => $request->product_price,
                            "color"     => $request->color,
                            "size"      => $request->size,
                  );
            array_push($cart[$request->product_id],$productInfoArr);
            session()->put('cart', $cart);
            return redirect('/cart');
            
            // return redirect()->back()->with('success', 'Product added to cart successfully!');
        }