This may seem trivial, but I wanted some input. In implementing a binary tree in Java, should the node class be a separate class file independent of the BinaryTree class, or should it be a default class in the same class file as the BinaryTree class?

First Example: Node is in separate class file

BinaryTree.java

public class BinaryTree {
    ...
}

BinaryTreeNode.java

public class BinaryTreeNode {
    ...
}

Second Example: Node class is default class in same class file

public class BinaryTree {
    ....
}
class BinaryTreeNode {
    ...
}

I almost never see the use case for putting more than one class inside of the same class file, but this might be the first time I see it being useful. Does this make sense, or would this be considered sloppy code?