'Make drop down list

I have a window for device filters (as in the photo_1). This window contains all the elements of the 'Select a brand', 'Select a OS', 'Presence' lists at once.

But the more elements in these lists, the larger my device filter window gets. I'd like to initially hide the list items, and make them a dropdown list (like in the photo_2).

Below is the part of the code that is responsible for displaying the list. How can I modify this code to add a drop down list?

  .......
  @override
  Widget build(BuildContext context) {
    return SimpleDialog(
      title: const Text('Filters'),
      contentPadding: const EdgeInsets.all(16),
      children: [
        Column(
          mainAxisSize: MainAxisSize.min,
          crossAxisAlignment: CrossAxisAlignment.stretch,
          children: [
            const Text('Select a brand'),
            ...brands.map((el) =>
                CustomCheckboxTile(
                  value: filters['brand']?.contains(el) ?? false,
                  label: el,
                  onChange:(check) => _handleCheckFilter(check, 'brand', el),
                ),
            ).toList(),
       .......