TYPO3 8.7.x / Extbase: How to get flexform select treeview values?

I'm using flexform for my extension plugin. There is a treeview from which I want to get the values at my controller. But I got only the amount of selected values with $this->settings['kategorien'].

<settings.kategorien>
    <TCEforms>
        <exclude>1</exclude>
        <label>Kategorien</label>
        <config>
            <type>select</type>
            <renderType>selectTree</renderType>
            <foreign_table>tx_myext_domain_model_adresskategorie</foreign_table>
            <foreign_table_where>ORDER BY kategoriename ASC</foreign_table_where>
            <size>20</size>
            <MM>tx_myext_domain_model_ttaddress_adresskategorie</MM>
            <treeConfig>
                <parentField>eltern</parentField>
                <appearance>
                    <expandAll>1</expandAll>
                    <showHeader>1</showHeader>
                </appearance>
            </treeConfig>
            <maxitems>1000</maxitems>
        </config>
    </TCEforms>
</settings.kategorien>

You have to remove <MM>tx_myext_domain_model_ttaddress_adresskategorie</MM>, since you work with a parentField in your tree configuration. If you want to use a MM table, you have to ensure the MM table meets the requirements