Are you developing a mobile or desktop application?
There isn't really the concept of expanding the sap.m.List as it's default behaviour is to navigate to another view.
If you are looking at a desktop application the Tree table might provide what you are looking for with a bit of styling.
https://sapui5.netweaver.ondemand.com/sdk/#test-resources/sap/ui/table/demokit/TreeTable.html
Regards,
Jason