addLeftItem method
Implementation
@override
void addLeftItem(IMindMapNode item) {
_leftItems.add(item);
item.setParentNode(this);
item.setNodeType(NodeType.left);
refresh();
//if (getNodeType() == NodeType.root && _leftItems.length == 1) {
getMindMap()?.refresh();
//}
// getMindMap()?.refresh();
getMindMap()?.onChanged();
}