It is better to use an Onchange method in these cases.

have also used onchange function like this

In xml file ->

<field name="type_selection" on_change="_set_list_data(type_selection)"/> -->

<field name="type_selection_2"/>

In python file ->

'type_selection': fields.selection([
                                  ('selection1','Selection 1'),
                                  ('selection2','Selection 2'),
                                  ('selection3','Selection 3')
                                  ],'Select Call Reason',required=False),
        'type_selection_2': fields.selection(
                                             _get_selection,
                                             'What do you want ?')

python function 

 def _set_list_data(self,cr,uid,selected,context=None):
        if selected == 'selection1':
            SELECTION_LIST = SELECTION_LIST_2
            vals = {'type_selection_2': SELECTION_LIST_2}        
            return {'type_selection_2': SELECTION_LIST_2}
        else:
            vals = {'type_selection_2': SELECTION_LIST_3}
            SELECTION_LIST = SELECTION_LIST_3        
            return {'type_selection_2': SELECTION_LIST_3}
        
    def _get_selection(self, cr, uid, context=None):
        return SELECTION_LIST

At first glance, there is a smell of (python) " Nested Lists".

But it will be helpful, if you give a concrete example, like for product's categories and subcategories, or Brand and Models of cars ...