1. Add all your upgrades
2. Sort them and group them by display_order like
100 Upgrade_monthly_one
110 Upgrade_monthly_two
120 Upgrade_monthly_three
200 Upgrade_yearly_one
210 Upgrade_yearly_two
220 Upgrade_yearly_three
Add 100, 200 (or only 200) to the option_field for groups
Now change your phrases!
(two groups with two titles and original title available_upgrades)
xc_aui_group_title_1
xc_aui_group_title_2
or
(two groups with one title and original title available_upgrades)
xc_aui_group_title_1
Change titles and text for top and bottom:
xc_aui_title_top
xc_aui_text_top
xc_aui_title_bottom
xc_aui_text_bottom
The result with 100, 200 looks like
Available Upgrades
xc_aui_group_title_1
100 Upgrade_monthly_one
110 Upgrade_monthly_two
120 Upgrade_monthly_three
xc_aui_group_title_2
200 Upgrade_yearly_one
210 Upgrade_yearly_two
220 Upgrade_yearly_three
If you dont like to have two titles
Available Upgrades
xc_aui_group_title_1
then you use only the second group:
add 200 to the option_field for groups
and change the phrase available_upgrades, then it will look like:
Available Upgrades
100 Upgrade_monthly_one
110 Upgrade_monthly_two
120 Upgrade_monthly_three
xc_aui_group_title_1
200 Upgrade_yearly_one
210 Upgrade_yearly_two
220 Upgrade_yearly_three
If you don't like my English, you are welcome to correct it!