insert method
Implementation
@override
void insert(int index, Object data, Style? style) {
assert(index == 0 || (index > 0 && index < length));
if (isNotEmpty) {
final child = queryChild(index, false);
child.node!.insert(child.offset, data, style);
return;
}
// empty
assert(index == 0);
final node = defaultChild;
add(node);
node?.insert(index, data, style);
}