Setting up WPF treeview triggers to show different images on expand

Question

I have a wpf tree view that displays nodes of various types with corresponding images such as folder images. Initially, the tree and its nodes with corresponding images display

Answer 1

For completeness, the original setup with the HierarchicalDataTemplate triggers just needed to use a RelativeSource binding (as indicated by HB's answer), such as:

Below is an example image with different images on expand in the TreeView: