The QML Settings property alias trick with a button group

[rs___]

I'm able to easily created persist text field settings using

Settings {
    property alias my_setting: my_setting_field.text
}
TextField {
    id: my_setting_field
}

I now need a setting that takes one of a set of possible values. I tried something like this

Settings {
    property alias my_setting: my_setting_group.checkedButton._value
}
ButtonGroup { id: my_setting_group }
Button {
    text: "option 1"
    property string _value: "option_1"
    checked: app_settings.my_setting === _value
    ButtonGroup.group: my_setting_group
}
Button {
    text: "option 2"
    property string _value: "option_2"
    checked: app_settings.my_setting === _value
    ButtonGroup.group: my_setting_group
}

and a few variations but couldn't get anything to work. Also, I would like a way to choose the default checked button when the app starts for the first time.