Example of unset not working properly

fruits.php

<?php
class Fruit_List {

	private $fruit = array();

	function __construct() {

		$this->add_fruit( array(
			1 => 'apple',
			2 => 'orange',
			3 => 'bananna',
			4 => 'pear',
		) );
		
		$this->fruit_list();

	}

	function add_fruit( $fruit = array() ) {
		$this->fruit = array_merge( $this->fruit, $fruit );
	}

	function fruit_list() {

		//* Delete 'pear'
		unset( $this->fruit[4] );

		echo '<ul>';
		foreach ( $this->fruit as $fruit ) {
			echo '<li>' . $fruit . '</li>';
		}
		echo '</ul>';

	}

}

new Fruit_List;