void insertAll(Iterable<OverlayEntry> entries, { OverlayEntry above })

Insert all the entries in the given iterable.

If above is non-null, the entries are inserted just above above. Otherwise, the entries are inserted on top.

Source 

void insertAll(Iterable<OverlayEntry> entries, { OverlayEntry above }) {
  assert(above == null || (above._overlay == this && _entries.contains(above)));
  if (entries.isEmpty)
    return;
  for (OverlayEntry entry in entries) {
    assert(entry._overlay == null);
    entry._overlay = this;
  }
  setState(() {
    int index = above == null ? _entries.length : _entries.indexOf(above) + 1;
    _entries.insertAll(index, entries);
  });
}