import 'package:flexible_tree_view/flexible_tree_view.dart';

FlexibleTreeView<String>(
	nodes: [
		TreeNode<String>(
			data: 'Cities', 
			expanded: true, 
			children: [
				TreeNode<String>(data: 'Beijing'), 
				TreeNode<String>(data: 'Shanghai'),
				TreeNode<String>(data: 'Tokyo'),
				TreeNode<String>(data: 'Paris')
			]
		)
	],
	nodeItemBuilder: (context, node) {
		return Padding(
			padding: const EdgeInsets.symmetric(vertical: 8),
			child: Row(
				children: [
				node.hasNodes
					? IconButton(
						iconSize: 12,
						splashRadius: 16,
						padding: EdgeInsets.zero,
						constraints:
							BoxConstraints.tight(Size(30, 30)),
						icon: Icon(node.expanded
							? Icons.remove
							: Icons.add),
						onPressed: () {
							node.expanded = !node.expanded;
						},
						)
					: const SizedBox(
						width: 12,
						),
				Text(
					node.data,
					style: TextStyle(
					fontSize: 12,
					color: Colors.black,
					),
					overflow: TextOverflow.ellipsis,
				)
				],
			));
	},
)