TwoLevelSublist({Key key, Widget leading, @required Widget title, Color backgroundColor, ValueChanged<bool> onOpenChanged, List<Widget> children: const [] })

Creates an item in a two-level list that can expland and collapse.

Source 

TwoLevelSublist({
  Key key,
  this.leading,
  @required this.title,
  this.backgroundColor,
  this.onOpenChanged,
  this.children: const <Widget>[],
}) : super(key: key);