docs(web): add Tree FAQ (#1998)

* docs(web): add `Tree` FAQ

* docs(web): update `Tree` FAQ and add information about unique values in `Tree` structure

docs/web/api/tree.en-US.md

@@ -111,3 +111,14 @@ Connects parent nodes in the tree with their child nodes at the same level. This
 ### Why doesn't the `onChange` callback return the value of the parent node when child node is selected in `valueMode = 'all'` mode?
 
 In `valueMode = 'all'` mode, the parent node will only appear in the selected values if all its child nodes are selected.
+
+### Why do other nodes get selected when I select a node?
+
+The `value` field of each item in the `data` array provided to the `Tree` component must be unique to avoid multiple selection issues caused by duplicate indices.
+
+### Why can't I expand nodes correctly even though I set `expanded`?
+
+The `value` field of each item in the `data` array provided to the `Tree` component must be unique to avoid incorrect expansion caused by duplicate indices.
+
+### Are `value` or unique `key` values in any level of the `Tree` structure non-repetitive?
+Yes, `value` or value defined by the alias `keys` in any level of the `Tree` structure are unique and non-repetitive.

docs/web/api/tree.md

@@ -115,3 +115,15 @@ spline: data
 ### 为什么在 `valueMode = 'all'` 模式下，选中子节点时 `onChange` 回调并没有返回父节点的值？
 
 在 `valueMode = 'all'` 模式下,必须当前子节点被全部选中后,父节点才会出现在选中值里面。
+
+### 为什么我选中了一个选中了一个节点，但是其他节点也有被选中的情况？
+
+提供给 `Tree` 组件的数组 `data` 数据中的每个 `value` 字段的值必须是唯一的，避免重复索引导致多选问题。
+
+### 为什么我设置了 `expanded` 却不能正确展开节点？
+
+提供给 `Tree` 组件的数组 `data` 数据中的每个 `value` 字段的值必须是唯一的，避免重复索引导致不能正确展开。
+
+### `Tree` 中任意一级结构中的 `value` 或唯一 `key` 值都不可重复吗？
+
+是的, 在 `Tree` 中任意一级结构中的 `value` 或使用 `keys` 别名定义的 `value` 值都是唯一的，不可重复。