http://dennisgaravsky.blogspot.com/2015/10/conditional-formatting-for-winforms.html

T291012_TreeListEditor.cs

using System;
using System.IO;
using DevExpress.Utils;
using DevExpress.ExpressApp;
using System.ComponentModel;
using DevExpress.ExpressApp.Model;
using DevExpress.Utils.Serializing;
using DevExpress.ExpressApp.TreeListEditors.Win;
using DevExpress.XtraTreeList.StyleFormatConditions;

namespace YourSolution.Module.Win.Controllers {
	// For more typical usage scenarios, be sure to check out https://documentation.devexpress.com/eXpressAppFramework/clsDevExpressExpressAppViewControllertopic.aspx.
	public class T291012_TreeListEditor : ViewController<ListView>, IModelExtender {
		TreeListFormatRulesStore formatRulesStore = null;
		TreeListEditor treeListEditor = null;
		protected override void OnActivated() {
			base.OnActivated();
			treeListEditor = View.Editor as TreeListEditor;
			if(treeListEditor != null) {
				View.ControlsCreated += View_ControlsCreated;
				View.ModelSaved += View_ModelSaved;
			}
		}
		private void View_ControlsCreated(object sender, EventArgs e) {
			treeListEditor.TreeList.Load += TreeList_Load;
		}
		private void InitializeFormatRules() {
			treeListEditor.TreeList.OptionsMenu.ShowConditionalFormattingItem = true;
			formatRulesStore = new TreeListFormatRulesStore() { FormatRules = treeListEditor.TreeList.FormatRules };
			formatRulesStore.Restore(((IModelListViewTreeFormatRuleSettings)View.Model).TreeFormattingSettings);
		}
		void TreeList_Load(object sender, EventArgs e) {
			InitializeFormatRules();
		}
		void View_ModelSaved(object sender, EventArgs e) {
			((IModelListViewTreeFormatRuleSettings)View.Model).TreeFormattingSettings = formatRulesStore.Save();
		}
		protected override void OnDeactivated() {
			if(treeListEditor != null) {
				if(treeListEditor.TreeList != null) {
					treeListEditor.TreeList.Load -= TreeList_Load;
				}
				View.ModelSaved -= View_ModelSaved;
				View.ControlsCreated -= View_ControlsCreated;
				treeListEditor = null;
			}
			base.OnDeactivated();
		}
		public void ExtendModelInterfaces(ModelInterfaceExtenders extenders) {
			extenders.Add<IModelListView, IModelListViewTreeFormatRuleSettings>();
		}
	}
	public interface IModelListViewTreeFormatRuleSettings {
		[Browsable(false)]
		string TreeFormattingSettings { get; set; }
	}
	//Dennis: This is a modified version of the solution given at https://www.devexpress.com/Support/Center/Question/Details/T289562 that can save/load settings into/from a string.
	internal class TreeListFormatRulesStore : IXtraSerializable {
		TreeListFormatRuleCollection formatRules;
		[DesignerSerializationVisibility(DesignerSerializationVisibility.Content), Browsable(true),
		 XtraSerializableProperty(XtraSerializationVisibility.Collection, true, false, true, 1000, XtraSerializationFlags.DefaultValue)]
		public virtual TreeListFormatRuleCollection FormatRules {
			get { return formatRules; }
			set { formatRules = value; }
		}
		public string Save() {
			using(MemoryStream stream = new MemoryStream()) {
				SaveCore(new XmlXtraSerializer(), stream);
				return Convert.ToBase64String(stream.GetBuffer());
			}
		}
		public void Restore(string settings) {
			if(!string.IsNullOrEmpty(settings)) {
				using(MemoryStream stream = new MemoryStream(Convert.FromBase64String(settings))) {
					RestoreCore(new XmlXtraSerializer(), stream);
				}
			}
		}
		void SaveCore(XtraSerializer serializer, object path) {
			Stream stream = path as Stream;
			if(stream != null)
				serializer.SerializeObject(this, stream, GetType().Name);
			else
				serializer.SerializeObject(this, path.ToString(), GetType().Name);
		}
		void RestoreCore(XtraSerializer serializer, object path) {
			Stream stream = path as Stream;
			if(stream != null)
				serializer.DeserializeObject(this, stream, GetType().Name);
			else
				serializer.DeserializeObject(this, path.ToString(), GetType().Name);
		}
		void XtraClearFormatRules(XtraItemEventArgs e) { FormatRules.Clear(); }
		object XtraCreateFormatRulesItem(XtraItemEventArgs e) {
			var rule = new TreeListFormatRule();
			formatRules.Add(rule);
			return rule;
		}
		#region IXtraSerializable
		public void OnEndDeserializing(string restoredVersion) { }
		public void OnEndSerializing() { }
		public void OnStartDeserializing(LayoutAllowEventArgs e) { }
		public void OnStartSerializing() { }
		#endregion
	}
}