Questa è la screen.



Quando seleziono il treeview, modifico la proprietà ImageList inserendo l'ImageList che ho creato io, visual studio automaticamente assegna a tutti i nodi esistenti l'immagine che sta nella posizione zero dell'ImageList. Questo è il codice Designer


codice:
        #region Codice generato da Progettazione Windows Form

        /// <summary>
        /// Metodo necessario per il supporto della finestra di progettazione. Non modificare
        /// il contenuto del metodo con l'editor di codice.
        /// </summary>
        public void InitializeComponent()
        {
            this.components = new System.ComponentModel.Container();
            System.Windows.Forms.ImageList imageList1;
            System.ComponentModel.ComponentResourceManager resources = new System.ComponentModel.ComponentResourceManager(typeof(Form1));
            System.Windows.Forms.TreeNode treeNode1 = new System.Windows.Forms.TreeNode("Nodo6");
            System.Windows.Forms.TreeNode treeNode2 = new System.Windows.Forms.TreeNode("Nodo11");
            System.Windows.Forms.TreeNode treeNode3 = new System.Windows.Forms.TreeNode("Nodo7", new System.Windows.Forms.TreeNode[] {
            treeNode2});
            System.Windows.Forms.TreeNode treeNode4 = new System.Windows.Forms.TreeNode("Nodo8");
            System.Windows.Forms.TreeNode treeNode5 = new System.Windows.Forms.TreeNode("Nodo0", new System.Windows.Forms.TreeNode[] {
            treeNode1,
            treeNode3,
            treeNode4});
            System.Windows.Forms.TreeNode treeNode6 = new System.Windows.Forms.TreeNode("Nodo9");
            System.Windows.Forms.TreeNode treeNode7 = new System.Windows.Forms.TreeNode("Nodo16");
            System.Windows.Forms.TreeNode treeNode8 = new System.Windows.Forms.TreeNode("Nodo10", new System.Windows.Forms.TreeNode[] {
            treeNode7});
            System.Windows.Forms.TreeNode treeNode9 = new System.Windows.Forms.TreeNode("Nodo1", new System.Windows.Forms.TreeNode[] {
            treeNode6,
            treeNode8});
            System.Windows.Forms.TreeNode treeNode10 = new System.Windows.Forms.TreeNode("Nodo2");
            System.Windows.Forms.TreeNode treeNode11 = new System.Windows.Forms.TreeNode("Nodo12");
            System.Windows.Forms.TreeNode treeNode12 = new System.Windows.Forms.TreeNode("Nodo15");
            System.Windows.Forms.TreeNode treeNode13 = new System.Windows.Forms.TreeNode("Nodo13", new System.Windows.Forms.TreeNode[] {
            treeNode12});
            System.Windows.Forms.TreeNode treeNode14 = new System.Windows.Forms.TreeNode("Nodo3", new System.Windows.Forms.TreeNode[] {
            treeNode11,
            treeNode13});
            System.Windows.Forms.TreeNode treeNode15 = new System.Windows.Forms.TreeNode("Nodo14");
            System.Windows.Forms.TreeNode treeNode16 = new System.Windows.Forms.TreeNode("Nodo4", new System.Windows.Forms.TreeNode[] {
            treeNode15});
            this.treeView1 = new System.Windows.Forms.TreeView();
            imageList1 = new System.Windows.Forms.ImageList(this.components);
            this.SuspendLayout();
            // 
            // imageList1
            // 
            imageList1.ImageStream = ((System.Windows.Forms.ImageListStreamer)(resources.GetObject("imageList1.ImageStream")));
            imageList1.TransparentColor = System.Drawing.Color.Transparent;
            imageList1.Images.SetKeyName(0, "120px-Flag_of_Bangladesh.svg.png");
            imageList1.Images.SetKeyName(1, "120px-Flag_of_the_Bahamas.svg.png");
            imageList1.Images.SetKeyName(2, "120px-Flag_of_Algeria.svg.png");
            imageList1.Images.SetKeyName(3, "120px-Flag_of_Austria.svg.png");
            // 
            // treeView1
            // 
            this.treeView1.ImageIndex = 0;
            this.treeView1.ImageList = imageList1;
            this.treeView1.Location = new System.Drawing.Point(105, 59);
            this.treeView1.Name = "treeView1";
            treeNode1.Name = "Nodo6";
            treeNode1.Text = "Nodo6";
            treeNode2.Name = "Nodo11";
            treeNode2.Text = "Nodo11";
            treeNode3.Name = "Nodo7";
            treeNode3.Text = "Nodo7";
            treeNode4.Name = "Nodo8";
            treeNode4.Text = "Nodo8";
            treeNode5.Name = "Nodo0";
            treeNode5.Text = "Nodo0";
            treeNode6.Name = "Nodo9";
            treeNode6.Text = "Nodo9";
            treeNode7.Name = "Nodo16";
            treeNode7.Text = "Nodo16";
            treeNode8.ImageKey = "120px-Flag_of_Bangladesh.svg.png";
            treeNode8.Name = "Nodo10";
            treeNode8.SelectedImageIndex = 0;
            treeNode8.Text = "Nodo10";
            treeNode9.ImageIndex = 1;
            treeNode9.Name = "Nodo1";
            treeNode9.Text = "Nodo1";
            treeNode10.ImageKey = "120px-Flag_of_Algeria.svg.png";
            treeNode10.Name = "Nodo2";
            treeNode10.Text = "Nodo2";
            treeNode11.Name = "Nodo12";
            treeNode11.Text = "Nodo12";
            treeNode12.Name = "Nodo15";
            treeNode12.Text = "Nodo15";
            treeNode13.Name = "Nodo13";
            treeNode13.Text = "Nodo13";
            treeNode14.ImageKey = "120px-Flag_of_Austria.svg.png";
            treeNode14.Name = "Nodo3";
            treeNode14.Text = "Nodo3";
            treeNode15.Name = "Nodo14";
            treeNode15.Text = "Nodo14";
            treeNode16.Name = "Nodo4";
            treeNode16.Text = "Nodo4";
            this.treeView1.Nodes.AddRange(new System.Windows.Forms.TreeNode[] {
            treeNode5,
            treeNode9,
            treeNode10,
            treeNode14,
            treeNode16});
            this.treeView1.SelectedImageIndex = 0;
            this.treeView1.Size = new System.Drawing.Size(345, 198);
            this.treeView1.TabIndex = 0;
            // 
            // Form1
            // 
            this.AutoScaleDimensions = new System.Drawing.SizeF(6F, 13F);
            this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font;
            this.ClientSize = new System.Drawing.Size(528, 371);
            this.Controls.Add(this.treeView1);
            this.Name = "Form1";
            this.Text = "Form1";
            this.ResumeLayout(false);

        }