Ability to validate if there are selected,checked, expanded items, if a node has items
I fully understand your disappointment. However, please note that the RadTreeView control is actually a navigation control. Also, the scenarios where it can be used for editing are not common. This is the reason why the data validation is not yet supported out of the box. On the other hand you can use the validation feature of our RadMaskedInput controls. You can use for example the RadMaksedTextInput control and set it as ItemEditTemplate of the RadTreeView control.
Honestly, a RAD data visualization control is unfinished if it doesn't support IDataErrorInfo and I really wouldn't call this a feature request. Like a lot of developers I bought this control suite to save time and leave the complex, fancy & slick xaml & control coding to Telerik experts.
Basic and simple requirement of all controls IMHO. Not sure why it wasn't there from day one...
this has great utility when using the TreeView as a multi-select checkbox control and one wishes to make the selection of at least one item a requirement.