private JComponent buildComponent() {
		JPanel container = new JPanel(new BorderLayout());

		splitPane = new JSplitPane(JSplitPane.HORIZONTAL_SPLIT);

		incomingTree = createTree();
		outgoingTree = createTree();
		GTreeSelectionListener treeSelectionListener = e -> {
			if (e.getEventOrigin() != EventOrigin.USER_GENERATED) {
				return;
			}

			if (!navigationOutgoingAction.isSelected()) {
				return;
			}

			if (currentFunction == null) {
				return;
			}

			TreePath path = e.getPath();
			if (path == null) {
				return;
			}

			CallNode node = (CallNode) path.getLastPathComponent();
			Address sourceAddress = node.getSourceAddress();
			goTo(new ProgramLocation(currentProgram, sourceAddress));
		};
		outgoingTree.addGTreeSelectionListener(treeSelectionListener);
		incomingTree.addGTreeSelectionListener(treeSelectionListener);

		GTreeSelectionListener contextSelectionListener = e -> notifyContextChanged();
		incomingTree.addGTreeSelectionListener(contextSelectionListener);
		outgoingTree.addGTreeSelectionListener(contextSelectionListener);
		splitPane.setLeftComponent(createTreePanel(true, incomingTree));
		splitPane.setRightComponent(createTreePanel(false, outgoingTree));

		splitPane.addHierarchyListener(new HierarchyListener() {
			@Override
			public void hierarchyChanged(HierarchyEvent e) {
				long changeFlags = e.getChangeFlags();
				if (HierarchyEvent.DISPLAYABILITY_CHANGED == (changeFlags &
					HierarchyEvent.DISPLAYABILITY_CHANGED)) {

					// check for the first time we are put together
					if (splitPane.isDisplayable()) {
						SwingUtilities.invokeLater(() -> splitPane.setDividerLocation(.5));
						splitPane.removeHierarchyListener(this);
					}
				}
			}
		});

		container.add(splitPane, BorderLayout.CENTER);

		incomingTree.setAccessibleNamePrefix("Incoming Function Calls");
		outgoingTree.setAccessibleNamePrefix("Outgoing Function Calls");

		return container;
	}
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