折线树图（polyline-tree)折叠时折线没有被折叠

### Version
5.0.0-beta.2

### Reproduction link
[https://echarts.apache.org/examples/zh/editor.html?c=tree-polyline](https://echarts.apache.org/examples/zh/editor.html?c=tree-polyline)

### Steps to reproduce
1.官网实例中的折叠树图https://echarts.apache.org/examples/zh/editor.html?c=tree-polyline
2.点击data的第一个下属节点，converters
3.依次点击flare的所有下属节点（data、display、flex、query、scale)
4.点击flare将所有内容折叠

### What is expected?
全部内容折叠后树表中没有多余的线

### What is actually happening?
全部内容折叠后树表留下五条分支线，相当于只折叠了节点和节点标签

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希望tree表的折线多一个圆角的配置项，就分支的上下两边有圆角

Reproduce the折线树图 example from the linked ECharts editor and follow the tree polyline rendering and collapse behavior. Done means collapsing the described nodes leaves no extra branch lines; the requested rounded-corner configuration is a separate scope to clarify.

Written by the indexing model from the issue text.