JAVA BINARY TREE OPERATION Please Help!

I've been working on a java program that'll store words and their definition in a binary tree alphabetically. I am just learning so I apologize for my confusion. There are several operations throughout this project but just for right now, I am stuck on how I would insert a word into the BST. I have three classes: Main (takes in the word and definition from the user), Dictionary, and DefinitionNode (stores helper methods). I am not to add additional fields or public methods but can add private methods. I have posted the Dictionary and DefinitionNode classes below with respective fields, methods, and constructor. I think it'll also involve recursion to continually check both left and right. Thank you for the help in advance!

Dictionary

private DefinitionNode root; // the root definition in the BST

/**

* Inserts a new word along with its meaning into the dictionary.

* @param word The word to be inserted

* @param meaning The meaning of the word being inserted

* @throws IllegalArgumentException when the word is already in this dictionary

*/

public void insert(String word, String meaning) throws IllegalArgumentException {

// implement using the DefinitionNode's insertHelper() method

}

DefinitionNode

private final String word; // the word this definition defines

private final String meaning; // the meaning of that word

private DefinitionNode leftChild; // nodes preceding this one alphabetically

private DefinitionNode rightChild; // nodes following this one alphabetically

/**

* Constructs a DefinitionNode with the specified word and meaning.

* @param word The word associated with this definition

* @param meaning The meaning of that word

* @throws IllegalArgumentException when the word or meaning are either

* references to an empty string or null references.

*/

public DefinitionNode(String word, String meaning) { }

/**

* This helper method inserts a new node into the tree or subtree that is

* rooted at this node. If it cannot directly add the new node as a child

* of this node, then it must recursively call this method on its appropriate

* child, to eventually complete this insertion.

* @param newNode The new node that is being inserted into the tree

* @throws IllegalArgumentException when the word inside newNode is already in

* the tree. Multiple definitions for the same word are not allowed.

*/

public void insertHelper(DefinitionNode newNode) throws IllegalArgumentException { }