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?

Your isEmpty() method does not seem to make sense to me.

It asks whether the parent is null. What has that got to do with being empty?

"Is the parent null?" means "am I the root?".

Or to say it differently - the root never has a parent, so per your test, root.isEmpty() is permanently true.

To my way of thinking, "empty tree" means "no children" (and "no data here" if that's a possibility).

If you don't have any children the ArrayList is never fulfilled, so why not just change it to:

public boolean isEmpty()
{
   return children.isEmpty();
}

Also, you should remove the (true) condition, from this:

if(root.isEmpty())
{
    if(true)
    {
       System.out.println("The tree is empty.");
    }
 }

to:

if(root.isEmpty())
    System.out.println("The tree is empty.");

If you wish to just output the result (as seen on the comments) you could also do some fancy java sh** like:

System.out.println(root.isEmpty()?"Empty":"Not empty");