转载：
https://documentation.devexpress.com/#WindowsForms/DevExpressXtraTreeListTreeList_CustomDrawNodeButtontopic
1.修改节点图标
(1)拖入TreeList控件(这里如何加载数据就不多说了哈)和ImageLIst控件
a.给ImageList添加图像
b.修改TreeList控件的属性
(2).在属性栏找到TreeList控件的CustomDrawNodeImages事件，并添加以下代码
private void treeList1_CustomDrawNodeImages(object sender, DevExpress.XtraTreeList.CustomDrawNodeImagesEventArgs e)
{
if (e.Node.Nodes.Count > )
{
if (e.Node.Expanded)
{
e.SelectImageIndex = ;
return;
}
e.SelectImageIndex = ;
}
else
{
e.SelectImageIndex = ;
}
}
(3)完成
2.修改按钮样式
在TreeList控件属性栏找到CustomDrawNodeButton事件，并添加以下代码
private void treeList1_CustomDrawNodeButton(object sender, DevExpress.XtraTreeList.CustomDrawNodeButtonEventArgs e)
{
Rectangle rect = Rectangle.Inflate(e.Bounds, , -); // painting background
Brush backBrush = new LinearGradientBrush(rect, Color.Blue, Color.LightSkyBlue,
LinearGradientMode.ForwardDiagonal); //填充指定矩形内部
e.Graphics.FillRectangle(backBrush, rect); //绘画3D边框
ControlPaint.DrawBorder3D(e.Graphics, rect, Border3DStyle.RaisedOuter); //要显示的图画
string displayCharacter = e.Expanded ? "-" : "+"; //水平,垂直居中
StringFormat outCharacterFormat = new StringFormat();
outCharacterFormat.Alignment = StringAlignment.Center;
outCharacterFormat.LineAlignment = StringAlignment.Center; //绘画图标
e.Graphics.DrawString(displayCharacter, new Font("Verdana", , FontStyle.Bold),
new SolidBrush(Color.White), rect, outCharacterFormat); // 禁止默认的图标显示
e.Handled = true;
}