how to return multiple collection in collection() and map it in map(): array

[timotiushadi]

public function collection()
    {
        $selling_transaction = SellingTransaction::with['product', 'product.supplier', 'product_selling_transaction'])
            ->whereYear('created_at', $this->year)
            ->whereMonth('created_at', $this->month)
            ->get();

        $suppliers = Supplier::with(['in_supplier_product_transaction'])
            ->get();

        // Return both collections to pass to map function
        $data = [
            'selling_transaction' => $selling_transaction,
            'suppliers' = $suppliers
        ]);

        return $data;
    }

public function map($data): array
    {
        dd($data);
    }

When I try to dd the data, it only contains the selling_transaction. Supplier data wasnt included