The views.tree option is undocumented on https://docs.telerik.com/kendo-ui/api/javascript/ui/filemanager/configuration/views.tree

The example fails with error:

Error: Error! The requested URL returned 0 - error at line 114

It's also unclear whether "tree" is a 3rd view in parallel to "list" and "grid" as the drop-down on https://demos.telerik.com/kendo-ui/filemanager/api would suggest (and if that is the case, how to enable this as an option in the toolbar) or whether it relates to the treeView of folders on the side.