Submenus generated from tab fields. Add submenu parameter to field and tab will become splitted with addition menus
'tab_1' => array(
//----And its name obviously
'name' => esc_html__( 'Tab 1', 'my-domain' ),
'label' => esc_html__( 'Tab 1 Label ', 'my-domain' ),
'icon' => 'fa fa-camera',
'fields' => array(
//field key and its settings. Full info about fields read in documentation.
'field' => array(
'type' => 'text',
'label' => esc_html__( 'Text 1', 'my-domain' ),
'submenu' => esc_html__( 'Submenu 1', 'my-domain' ),
),
'field_2' => array(
'type' => 'text',
'label' => esc_html__( 'Text 2', 'my-domain' ),
'submenu' => esc_html__( 'Submenu 2', 'my-domain' ),
),
'field_3' => array(
'type' => 'text',
'label' => esc_html__( 'Text 3', 'my-domain' ),
'submenu' => esc_html__( 'Submenu 3', 'my-domain' ),
),
'field_4' => array(
'type' => 'text',
'label' => esc_html__( 'Text 4', 'my-domain' ),
'submenu' => esc_html__( 'Submenu 4', 'my-domain' ),
),
)
),