Remove TreeViewHelper and shorten the code so the extra struct is not needed.

src/Avalonia.Controls/TreeView.cs

@@ -554,6 +554,54 @@ namespace Avalonia.Controls
             }
         }
 
+        /// <summary>
+        /// Find which node is first in hierarchy.
+        /// </summary>
+        /// <param name="treeView">Search root.</param>
+        /// <param name="nodeA">Nodes to find.</param>
+        /// <param name="nodeB">Node to find.</param>
+        /// <returns>Found first node.</returns>
+        private static TreeViewItem FindFirstNode(TreeView treeView, TreeViewItem nodeA, TreeViewItem nodeB)
+        {
+            return FindInContainers(treeView.ItemContainerGenerator, nodeA, nodeB);
+        }
+
+        private static TreeViewItem FindInContainers(ITreeItemContainerGenerator containerGenerator,
+            TreeViewItem nodeA,
+            TreeViewItem nodeB)
+        {
+            IEnumerable<ItemContainerInfo> containers = containerGenerator.Containers;
+
+            foreach (ItemContainerInfo container in containers)
+            {
+                TreeViewItem node = FindFirstNode(container.ContainerControl as TreeViewItem, nodeA, nodeB);
+
+                if (node != null)
+                {
+                    return node;
+                }
+            }
+
+            return null;
+        }
+
+        private static TreeViewItem FindFirstNode(TreeViewItem node, TreeViewItem nodeA, TreeViewItem nodeB)
+        {
+            if (node == null)
+            {
+                return null;
+            }
+
+            TreeViewItem match = node == nodeA ? nodeA : node == nodeB ? nodeB : null;
+
+            if (match != null)
+            {
+                return match;
+            }
+
+            return FindInContainers(node.ItemContainerGenerator, nodeA, nodeB);
+        }
+
         /// <summary>
         /// Returns all items that belong to containers between <paramref name="from"/> and <paramref name="to"/>.
         /// The range is inclusive.
@@ -569,7 +617,7 @@ namespace Avalonia.Controls
                 return items;
             }
 
-            TreeViewItem firstItem = TreeViewHelper.FindFirstNode(this, new TreeViewHelper.SearchInfo(from, to));
+            TreeViewItem firstItem = FindFirstNode(this, from, to);
 
             if (firstItem == null)
             {

src/Avalonia.Controls/TreeViewHelper.cs

@@ -1,90 +0,0 @@
-// Copyright (c) The Avalonia Project. All rights reserved.
-// Licensed under the MIT license. See licence.md file in the project root for full license information.
-
-using System.Collections.Generic;
-using Avalonia.Controls.Generators;
-
-namespace Avalonia.Controls
-{
-    /// <summary>
-    /// Helper for <see cref="TreeView"/> related operations.
-    /// </summary>
-    internal static class TreeViewHelper
-    {
-        /// <summary>
-        /// Find which node from search info is first in hierarchy.
-        /// </summary>
-        /// <param name="treeView">Search root.</param>
-        /// <param name="searchInfo">Nodes to search for.</param>
-        /// <returns>Found first node.</returns>
-        public static TreeViewItem FindFirstNode(TreeView treeView, in SearchInfo searchInfo)
-        {
-            return FindInContainers(treeView.ItemContainerGenerator, in searchInfo);
-        }
-
-        private static TreeViewItem FindInContainers(ITreeItemContainerGenerator containerGenerator,
-            in SearchInfo searchInfo)
-        {
-            IEnumerable<ItemContainerInfo> containers = containerGenerator.Containers;
-
-            foreach (ItemContainerInfo container in containers)
-            {
-                TreeViewItem node = FindFirstNode(container.ContainerControl as TreeViewItem, in searchInfo);
-
-                if (node != null)
-                {
-                    return node;
-                }
-            }
-
-            return null;
-        }
-
-        private static TreeViewItem FindFirstNode(TreeViewItem node, in SearchInfo searchInfo)
-        {
-            if (node == null)
-            {
-                return null;
-            }
-
-            TreeViewItem match = searchInfo.GetMatch(node);
-
-            if (match != null)
-            {
-                return match;
-            }
-
-            return FindInContainers(node.ItemContainerGenerator, in searchInfo);
-        }
-
-        /// <summary>
-        /// Node search info.
-        /// </summary>
-        public readonly struct SearchInfo
-        {
-            public readonly TreeViewItem Search1;
-            public readonly TreeViewItem Search2;
-
-            public SearchInfo(TreeViewItem search1, TreeViewItem search2)
-            {
-                Search1 = search1;
-                Search2 = search2;
-            }
-
-            public TreeViewItem GetMatch(TreeViewItem candidate)
-            {
-                if (candidate == Search1)
-                {
-                    return Search1;
-                }
-
-                if (candidate == Search2)
-                {
-                    return Search2;
-                }
-
-                return null;
-            }
-        }
-    }
-}