It seems like ExtJs 6 looks good and fast, because there are still myriads of bugs. For example, I cannot add a vertical scrollbar to the treepanel. As a result when there are too many nodes, I'm unable to scroll through all of them. This is what I tried:
scrollable: true, // <-- Does not work!
autoScroll: true, // <-- Does not work!
I wonder why such primitive things stopped working in modern ExtJs. I hope there is some magic mantra that can fix it.