@php
    $def = (object)['id'=>'', 'department_name'=>'', 'level'=>1, 'parent_department_id'=>''];
    $merged = collect([$def])->merge($departments); // ← $items を $departments に変更
    $selected = fn($val) => ($val == $value) ? 'selected' : '';
    $attr['class'] = 'input-select w-full';
@endphp

<select name='{{$name}}' id="{{$name}}" {!! $attributes->merge($attr) !!}>
    @foreach($merged as $dep)
        <option value="{{ $dep->id }}" {{ $selected($dep->id) }}>
            {{ str_repeat('　', $dep->level - 1) }}{{ $dep->department_name }}
        </option>
    @endforeach
</select>