Hi Raj Sharma,
When inheriting from RadTreeView you also need to override ThemeClassName property and return the full name of the RadTreeView type. For example:
public class MyTreeView : RadTreeView
public override string ThemeClassName
base.ThemeClassName = value;
The expand collapse images are most likely not being shown because they are set through styles and the themes for RadTreeView are not valid for your type. Overriding the ThemeClassName property should do the trick. Please write again if you have other questions.
the Telerik team
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