Change of icon on expanding a group in expandable list view android

Question

how do I change the icon of a group when it is expanded. I'm putting the icons for the group in the on-create method only

MenuItems item = new MenuItems(0, R.drawable.minus, "HOME");
listDataHeader.add(item);
item = new MenuItems(1, R`enter code here`.drawable.plus, "SH");
listDataHeader.add(item);
item = new MenuItems(2, R.drawable.minus, "AT");
listDataHeader.add(item);