Use description for parent paths

Testing https://github.com/Microsoft/vscode/issues/64262

![image](https://user-images.githubusercontent.com/10746682/49509234-03a0aa80-f885-11e8-88fe-81ff28bd3389.png)


![image](https://user-images.githubusercontent.com/10746682/49509286-2af77780-f885-11e8-8e36-d1a01e8fa29b.png)


TreeItem has description property which can be used for this