@Override
	protected void verticesAdded(Collection<FcgVertex> added) {
		for (FcgVertex v : added) {
			Function f = v.getFunction();
			verticesByFunction.put(f, v);
			verticesByLevel.get(v.getLevel()).add(v);
		}
		super.verticesAdded(added);
	}
Returns the largest level (the furthest level from the source node) in the given 
direction 

@param direction the direction to search
@return the largest level
Ghidra/Features/GraphFunctionCalls/src/main/java/functioncalls/graph/FunctionCallGraph.java