fix: Tree missing aniation when virtual scrolled (ant-design#20565)

* fix: Tree missing aniation when virtual scrolled

* clean up

* skip debug test

components/tree/Tree.tsx

@@ -206,6 +206,7 @@ export default class Tree extends React.Component<TreeProps, any> {
     const prefixCls = getPrefixCls('tree', customizePrefixCls);
     return (
       <RcTree
+        itemHeight={20}
         ref={this.setTreeRef}
         {...props}
         prefixCls={prefixCls}

components/tree/__tests__/demo.test.js

@@ -1,3 +1,3 @@
 import demoTest from '../../../tests/shared/demoTest';
 
-demoTest('tree');
+demoTest('tree', { skip: ['big-data.md'] });

components/tree/demo/big-data.md

@@ -0,0 +1,42 @@
+---
+order: 99
+title:
+  zh-CN: 大数据
+  en-US: Big data
+debug: true
+---
+
+## zh-CN
+
+大数据展示。
+
+## en-US
+
+Plenty of tree nodes.
+
+```jsx
+import { Tree } from 'antd';
+
+const treeData = [];
+
+for (let i = 0; i < 100; i += 1) {
+  const children = [];
+
+  for (let j = 0; j < 100; j += 1) {
+    children.push({
+      title: `child ${i}-${j}`,
+      key: `l-${i}-${j}`,
+    });
+  }
+
+  treeData.push({
+    title: `parent ${i}`,
+    key: `l-${i}`,
+    children,
+  });
+}
+
+const Demo = () => <Tree defaultExpandAll height={400} treeData={treeData} />;
+
+ReactDOM.render(<Demo />, mountNode);
+```