https://documentation.devexpress.com/#WindowsForms/DevExpressXtraTreeListTreeList_CustomDrawNodeButtontopic

private void treeList1_CustomDrawNodeImages(object sender, DevExpress.XtraTreeList.CustomDrawNodeImagesEventArgs e)        {            if (e.Node.Nodes.Count > 0)            {                if (e.Node.Expanded)                {                    e.SelectImageIndex = 2;                    return;                }                e.SelectImageIndex = 1;            }            else            {                e.SelectImageIndex = 0;            }        }

private void treeList1_CustomDrawNodeButton(object sender, DevExpress.XtraTreeList.CustomDrawNodeButtonEventArgs e)        {            Rectangle rect = Rectangle.Inflate(e.Bounds, 0, -2);            // 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", 8, FontStyle.Bold),              new SolidBrush(Color.White), rect, outCharacterFormat);            // 禁止默认的图标显示            e.Handled = true;        }