优化更新代码，添加界面功能并整合

WPFluent/Controls/TreeListView/TreeListViewItem.cs

@@ -0,0 +1,33 @@
+using System.Windows;
+
+namespace WPFluent.Controls;
+
+public class TreeListViewItem : TreeViewItem
+{
+    private int _level = -1;
+
+    /// <summary>
+    /// Item's hierarchy in the tree
+    /// </summary>
+    public int Level
+    {
+        get
+        {
+            if (_level == -1)
+            {
+                _level = (ItemsControlFromItemContainer(this) is TreeListViewItem parent) ? parent.Level + 1 : 0;
+            }
+            return _level;
+        }
+    }
+
+    protected override DependencyObject GetContainerForItemOverride()
+    {
+        return new TreeListViewItem();
+    }
+
+    protected override bool IsItemItsOwnContainerOverride(object item)
+    {
+        return item is TreeListViewItem;
+    }
+}