@Override
				public boolean isEnabledForContext(ActionContext context) {
					if (currentFunction == null) {
						return false;
					}

					Object contextObject = context.getContextObject();
					if (!(contextObject instanceof GTree)) {
						return false;
					}

					GTree gTree = (GTree) contextObject;
					TreePath[] selectionPaths = gTree.getSelectionPaths();
					if (selectionPaths.length != 1) {
						return false;
					}
					CallNode node = ((CallNode) selectionPaths[0].getLastPathComponent());
					// remoteFunction can be null for dead-end nodes
					Function remoteFunction = node.getRemoteFunction();
					String menuName =
						SHOW_CALL_TREE_MENU_PREFIX +
							(remoteFunction == null ? "" : remoteFunction.getName());
					MenuData data = getPopupMenuData().cloneData();
					data.setMenuPath(new String[] { menuName });
					setPopupMenuData(data);
					return remoteFunction != null;
				}
A variable used to restrict open-ended operations, like expanding all nodes or filtering.
Ghidra/Features/Base/src/main/java/ghidra/app/plugin/core/calltree/CallTreeProvider.java