void buildNodeList() {
		synchronized (root) {
			nodeList.clear();
			Enumeration<? extends TreeNode> nodes = root.preorderEnumeration();
			while (nodes.hasMoreElements()) {
				nodeList.add((ProgramNode) nodes.nextElement());
			}
		}
	}
Build a list of ProgramNodes in preorder.
Ghidra/Features/Base/src/main/java/ghidra/app/plugin/core/programtree/ProgramDnDTree.java