How to check if arraylist tree in Java is empty or not?

I'm creating a tree in Java. And when I create a method to check if the tree is empty, it doesn't work correctly. When I debug the program, and get to the if statement that checks if root is empty or not, I keep getting "parent = null". I think the problem may be due to the parent set method, but I'm not sure. Here's my code:

{
    private Tree data = null; //create a tree
    private List<GeneralTree> children = new ArrayList<>(); //create an arraylist
    private GeneralTree parent = null; //create a parent
    public GeneralTree(Tree data) //constructor
    {
        this.data = data;
    }
    public void addChild(GeneralTree child) //create a child method to create a child
    {
        child.setParent(this);
        this.children.add(child);
    }
    public void addChild(Tree data) //create a method to put data into the children
    {
        GeneralTree<Tree> newChild = new GeneralTree<>(data);
        this.addChild(newChild);
    }
    public void addChildren(List<GeneralTree> children) //create a method to add children to a parent
    {
        for(GeneralTree t: children)
        {
            t.setParent(this);
        }
        this.children.addAll(children);
    }
    public List<GeneralTree> getChildren() //get the children
    {
        return this.children;
    }
    public Tree getData() //get the data in the children
    {
        return data;
    }
    public void setData(Tree data) //set the data of the children together
    {
        this.data = data;
    }
    public void setParent(GeneralTree parent) //set the parent together
    {
        this.parent = parent;
    }
    public GeneralTree getParent() //get the parent
    {
        return this.parent;
    }

Main isEmpty() method that I'm having trouble with

    public boolean isEmpty()
    {
        if(this.parent == null) //check if value is null. if it is true, the tree is full.
        {
            System.out.println("The tree is empty.");
            return false;
        }
        else
        {
            return true;
        }
    }

Main Method to drive the class

    public static void main(String[] args)
    {
        GeneralTree<String> root = new GeneralTree<>("Root"); //create a root node

        if(root.isEmpty())
        {
            if(true)
            {
                System.out.println("The tree is empty.");
            }
        }
        GeneralTree<String> child1 = new GeneralTree<>("Child 1"); //first child node
        child1.addChild("Grandchild 1"); //first grandchild node
        child1.addChild("Grandchild 2"); //second grandchild node
        GeneralTree<String> child2 = new GeneralTree<>("Child 2"); //second child node
        child2.addChild("Grandchild 3"); //third grandchild node
        root.addChild(child1);
        root.addChild(child2);
        root.addChild("Child 3"); //third child node
        root.addChildren(Arrays.asList(new GeneralTree<>("Child 4"), new GeneralTree<>("Child 5"), new GeneralTree<>("Child 6")));//add fourth, fifth, and sixth children nodes
        for(GeneralTree node: root.getChildren()) //get and print the children as long as they're under the root
        {
            System.out.println(node.getData()); //get the data
        }
    }
}

I don't know if the issue is with the parent node or the design of the isEmpty() method?