方法一：通过代码方式实现：

private string FilePath = Application.StartupPath + "\\Images\\";

         Image img = new Bitmap(FilePath + "one.ico");

         Image img1 = new Bitmap(FilePath + "two.ico");

         ImageList imgs = new ImageList();

         imgs.Images.Add(img);

         imgs.Images.Add(img1);

         this.tvTest.ImageList = imgs;

         TreeNode node = new TreeNode();

         node.Text = "Root";

         this.tvTest.Nodes.Add(node);

         node.ImageIndex = 0;

         node.SelectedImageIndex = 0;

         TreeNode node1 = new TreeNode();

         node1.Text = "root001";

         TreeNode node2 = new TreeNode();

         node2.Text = "root002";

         node.Nodes.Add(node1);

         node.Nodes.Add(node2);

         this.tvTest.ExpandAll();

         node1.ImageIndex =1;

         node1.SelectedImageIndex = 1;

         node2.ImageIndex = 1;

         node2.SelectedImageIndex = 1;

方法二：通过绑定ImageList控件实现

操作步骤：第一步，工具箱中拖动ImageList控件；

第二步，ImageList控件Images属性添加图片集合；

第三步，TreeView控件绑定ImageList属性；

第四步，代码如下所示：

TreeNode node = new TreeNode();

node.Text = "Root";

this.tvTest.Nodes.Add(node);

node.ImageIndex = 0;

node.SelectedImageIndex = 0;

TreeNode node1 = new TreeNode();

node1.Text = "root001";

TreeNode node2 = new TreeNode();

node2.Text = "root002";

node.Nodes.Add(node1);

node.Nodes.Add(node2);

this.tvTest.ExpandAll();

node1.ImageIndex =1;

node1.SelectedImageIndex = 1;

node2.ImageIndex = 1;

node2.SelectedImageIndex = 1;