@Override
	public void actionPerformed(ActionContext context) {
		GTree gTree = (GTree) context.getContextObject();
		TreePath[] selectionPaths = gTree.getSelectionPaths();
		for (TreePath path : selectionPaths) {
			GTreeNode node = (GTreeNode) path.getLastPathComponent();
			gTree.expandTree(node);
		}
	}
Only shows up if all selected nodes are expandable.
Ghidra/Features/Base/src/main/java/ghidra/app/plugin/core/datamgr/actions/ExpandAllAction.java