Sorry for the inconvenience caused.
In TreeView, currently there isn’t support for event while performing expand action on TreeView nodes. We have already considered providing support for multiple events for the TreeView component in the Blazor platform. We will implement the events, NodeExpanding and NodeExpanded for node expand action and will include in our upcoming Blazor release, in the mid of August month. Until then, we appreciate your patience.
Please let us know if you have any queries.