Insert parent and child at once in Laravel 5.6

I am trying to insert data at once in my both users and user_details table. See below code:

Model:

class User extends Authenticatable
{
    public function user_detail() {
        return $this->hasOne('App\UserDetail', 'user_id');
    }
}

View:

<div class="form-group">
    {!! Form::label('username', 'Username:* ', ['class' => 'col-md-4 control-label']) !!}
    <div class="col-md-6">
        {!! Form::text('username', null, ['class' => 'form-control', 'required' => 'required']) !!}
        {!! $errors->first('username', '<p class="help-block">:message</p>') !!}
    </div>
</div>
...
<div class="form-group">
    {!! Form::label('user_detail[about_me]', 'About Me: ', ['class' => 'col-md-4 control-label']) !!}
    <div class="col-md-6">
        {!! Form::textarea('user_detail[about_me]', null, ['class' => 'form-control', 'required' => 'required']) !!}
        {!! $errors->first('user_detail[about_me]', '<p class="help-block">:message</p>') !!}
    </div>
</div>

Controller:

public function store(Request $request) {
    $data = $request->except('password'); //dd($data);
    $user = User::create($data);
    $user->user_detail->create($data['user_detail']);
}

Error Message:

In above I have posted my code(Removed rest fields. Keep only user table username and user_details about_me)

In my above code data inserted successfully in the users table but error occur while inserting in the child table.

Please look my code and suggest me how to insert record in my child table.

via Chebli Mohamed