The RadTreeView control have TriState checkbox support. In other words instead of two states (checked, unchecked), there are three (additional indeterminate state). Basically, if you have a tree view item with few child nodes and you check one of the nodes, the parent will go in indeterminate state. If all children are checked, the parent will be checked automatically. If you check the parent, all children will be checked automatically. You can take a look at the CheckBox Support
help article for more information on that matter.
However, note that the checkbox support has few known issues and this is why we recommend implementing custom checkbox functionality. You can see how to do it in the Implement a Tri-State CheckBox logic using MVVM
I hope this helps.
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