Inserting new Node in a Binary Search Tree
A BST must not contain duplicate values. 
Your implementation allows inserting a duplicate value as the right child.
It should be something like this:

if (newNode.getNodeData() &lt; currentParent.getNodeData()) {
    if (currentParent.getLeftChild() == null) {
        currentParent.setLeftChild(newNode);
    } else {
        insertNode(currentParent.getLeftChild(), newNode);
    }
} else if (newNode.getNodeData() &gt; currentParent.getNodeData()) {
    if (currentParent.getRightChild() == null) {
        currentParent.setRightChild(newNode);
    } else {
        insertNode(currentParent.getRightChild(), newNode);
    }
} else {
    // duplicate item
    // option 1: do nothing: ignore input, add nothing to the tree
    // option 2: throw new IllegalArgumentException("no no: dupe")
}


It's also recommended to use braces always,
so I modified the original code accordingly.