got legacy tree icons showing up now, added a couple of filters for this to work.

src/Umbraco.Core/Serialization/JsonCreationConverter.cs

@@ -4,33 +4,6 @@ using Newtonsoft.Json.Linq;
 
 namespace Umbraco.Core.Serialization
 {
-    /// <summary>
-    /// This is used in order to deserialize a json object on a property into a json string since the property's type is 'string'
-    /// </summary>
-    internal class JsonToStringConverter : JsonConverter
-    {
-        public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
-        {
-            throw new NotImplementedException();
-        }
-
-        public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
-        {
-            if (reader.ValueType == typeof(string))
-            {
-                return reader.Value;
-            }
-            // Load JObject from stream
-            JObject jObject = JObject.Load(reader);
-            return jObject.ToString();
-        }
-
-        public override bool CanConvert(Type objectType)
-        {
-            return typeof(string).IsAssignableFrom(objectType);
-        }
-    }
-
     internal abstract class JsonCreationConverter<T> : JsonConverter
     {
         /// <summary>

src/Umbraco.Core/Umbraco.Core.csproj

@@ -691,6 +691,7 @@
     <Compile Include="Serialization\IStreamedResult.cs" />
     <Compile Include="Serialization\JsonCreationConverter.cs" />
     <Compile Include="Serialization\JsonNetSerializer.cs" />
+    <Compile Include="Serialization\JsonToStringConverter.cs" />
     <Compile Include="Serialization\SerializationExtensions.cs" />
     <Compile Include="Serialization\SerializationService.cs" />
     <Compile Include="Serialization\StreamedResult.cs" />

src/Umbraco.Web.UI.Client/common/filters/treeiconclass.filter.js

@@ -0,0 +1,21 @@
+'use strict';
+
+define(['angular'], function (angular) {
+
+    /**
+    * @ngdoc filter 
+    * @name umbraco.filters:umbTreeIconClass
+    * @restrict E
+    * @description This will properly render the tree icon class based on the tree icon set on the server
+    **/
+    function treeIconClassFilter() {
+        return function (treeNode, standardClasses) {
+            if (treeNode.iconIsClass) {
+                return standardClasses + " " + treeNode.icon;
+            }
+            return standardClasses;
+        };
+    };
+    angular.module('umbraco.filters').filter("umbTreeIconClass", treeIconClassFilter);
+
+});

src/Umbraco.Web.UI.Client/common/filters/treeiconimage.filter.js

@@ -0,0 +1,21 @@
+'use strict';
+
+define(['angular'], function (angular) {
+
+    /**
+    * @ngdoc filter 
+    * @name umbraco.filters:umbTreeIconImage
+    * @restrict E
+    * @description This will properly render the tree icon image based on the tree icon set on the server
+    **/
+    function treeIconImageFilter() {
+        return function (treeNode) {
+            if (treeNode.iconIsClass) {
+                return "";
+            }
+            return "<img src='" + treeNode.iconFilePath + "'></img>";
+        };
+    };
+    angular.module('umbraco.filters').filter("umbTreeIconImage", treeIconImageFilter);
+
+});

src/Umbraco.Web.UI/umbraco/Views/common/tree.html

@@ -13,7 +13,8 @@
              ng-class="{'icon-caret-right': !node.expanded, 'icon-caret-down': node.expanded}" 
              ng-click="getTreeChildren(node)"></ins>
 
-        <i class="icon umb-tree-icon sprTree {{node.icon}}"></i>
+        <i class="{{node|umbTreeIconClass:'icon umb-tree-icon sprTree'}}" ng-bind-html-unsafe="node|umbTreeIconImage">            
+        </i>
 
         <a ng-href="#{{node.view}}">{{node.name}}</a>
         <i class="umb-options" ng-click="showContextMenu(node, $event)"><i></i><i></i><i></i></i>

src/Umbraco.Web.UI/umbraco/js/umbraco.filters.js

@@ -17,6 +17,38 @@ angular.module('umbraco.filters', [])
                 };
             });
 
+    /**
+    * @ngdoc filter 
+    * @name umbraco.filters:umbTreeIconImage
+    * @restrict E
+    * @description This will properly render the tree icon image based on the tree icon set on the server
+    **/
+    function treeIconImageFilter() {
+        return function (treeNode) {
+            if (treeNode.iconIsClass) {
+                return "";
+            }
+            return "<img src='" + treeNode.iconFilePath + "'></img>";
+        };
+    };
+    angular.module('umbraco.filters').filter("umbTreeIconImage", treeIconImageFilter);
+
+    /**
+    * @ngdoc filter 
+    * @name umbraco.filters:umbTreeIconClass
+    * @restrict E
+    * @description This will properly render the tree icon class based on the tree icon set on the server
+    **/
+    function treeIconClassFilter() {
+        return function (treeNode, standardClasses) {
+            if (treeNode.iconIsClass) {
+                return standardClasses + " " + treeNode.icon;
+            }
+            return standardClasses;
+        };
+    };
+    angular.module('umbraco.filters').filter("umbTreeIconClass", treeIconClassFilter);
+
 
     return app;
 });

src/Umbraco.Web/Trees/TreeNode.cs

@@ -1,6 +1,7 @@
 using System.Collections.Generic;
 using System.Runtime.Serialization;
 using Newtonsoft.Json;
+using Umbraco.Core.IO;
 
 namespace Umbraco.Web.Trees
 {
@@ -65,6 +66,33 @@ namespace Umbraco.Web.Trees
         [DataMember(Name = "icon")]
         public string Icon { get; set; }
 
+        /// <summary>
+        /// Returns true if the icon represents a CSS class instead of a file path
+        /// </summary>
+        [DataMember(Name = "iconIsClass")]
+        public bool IconIsClass
+        {
+            get
+            {
+                //if it starts with a '.' or doesn't contain a '.' at all then it is a class
+                return Icon.StartsWith(".") || Icon.Contains(".") == false;
+            }
+        }
+
+        /// <summary>
+        /// Returns the icon file path if the icon is not a class, otherwise returns an empty string
+        /// </summary>
+        [DataMember(Name = "iconFilePath")]
+        public string IconFilePath
+        {
+            get
+            {
+                return IconIsClass
+                           ? string.Empty
+                           : IOHelper.ResolveUrl("~/umbraco/images/umbraco/" + Icon);
+            }
+        }
+
         /// <summary>
         /// The URL path for the editor for this model
         /// </summary>

src/Umbraco.Web/Trees/TreeNodeCollection.cs

@@ -1,5 +1,6 @@
 using System.Collections.Generic;
 using System.Runtime.Serialization;
+using Newtonsoft.Json.Linq;
 
 namespace Umbraco.Web.Trees
 {

src/Umbraco.Web/Umbraco.Web.csproj

@@ -303,6 +303,7 @@
     <Compile Include="Trees\ApplicationTreeExtensions.cs" />
     <Compile Include="Trees\TreeNode.cs" />
     <Compile Include="Trees\TreeNodeCollection.cs" />
+    <Compile Include="Trees\TreeNodeSerializer.cs" />
     <Compile Include="Trees\TreeQueryStringParameters.cs" />
     <Compile Include="Trees\ApplicationTreeApiController.cs" />
     <Compile Include="Editors\BackOfficeController.cs" />