Icons in the tree view represent elements in the UML model. When you delete an icon from the tree view, you delete an element from the model and all the views of the element in diagrams.
Shapes in UML diagrams represent views of the model elements rather than the elements themselves. By default, when you delete a view of an element, the element is deleted from the diagram but not from the model.
You can change the default behavior so you are prompted when you attempt to delete any view of an element. The message that appears gives you the option to delete only the view or both the view and the model element.
Note: For some UML elements, such as a state, only one view can exist in a model. In these cases, deleting a view is the same as deleting the element from the model.