Steps to Reproduce

https://zkfiddle.org/sample/2db18el/2-Dynamic-Tree

scroll down in the tree to trigger loading additional tree rows

Current Result

during the delayed loading time the loading animation doesn't appear

Expected Result

render the loading animation as in listbox/grid

(added the style z-tree-loading manually)

Debug Information

the css class z-tree-loading already exists, and is added when the loading starts.
However it is removed before the onRender request is even sent to the server.

Workaround