final protected function _bind() {
		if ( $this->bound ) {
			return;
		}

		// Add the root node.
		// Clear it first, just in case. Don't mess with The Root.
		$this->remove_node( 'root' );
		$this->add_node(
			array(
				'id'    => 'root',
				'group' => false,
			)
		);

		// Normalize nodes: define internal 'children' and 'type' properties.
		foreach ( $this->_get_nodes() as $node ) {
			$node->children = array();
			$node->type     = ( $node->group ) ? 'group' : 'item';
			unset( $node->group );

			// The Root wants your orphans. No lonely items allowed.
			if ( ! $node->parent ) {
				$node->parent = 'root';
			}
		}

		foreach ( $this->_get_nodes() as $node ) {
			if ( 'root' == $node->id ) {
				continue;
			}

			// Fetch the parent node. If it isn't registered, ignore the node.
			$parent = $this->_get_node( $node->parent );
			if ( ! $parent ) {
				continue;
			}

			// Generate the group class (we distinguish between top level and other level groups).
			$group_class = ( $node->parent == 'root' ) ? 'ab-top-menu' : 'ab-submenu';

			if ( $node->type == 'group' ) {
				if ( empty( $node->meta['class'] ) ) {
					$node->meta['class'] = $group_class;
				} else {
					$node->meta['class'] .= ' ' . $group_class;
				}
			}

			// Items in items aren't allowed. Wrap nested items in 'default' groups.
			if ( $parent->type == 'item' && $node->type == 'item' ) {
				$default_id = $parent->id . '-default';
				$default    = $this->_get_node( $default_id );

				// The default group is added here to allow groups that are
				// added before standard menu items to render first.
				if ( ! $default ) {
					// Use _set_node because add_node can be overloaded.
					// Make sure to specify default settings for all properties.
					$this->_set_node(
						array(
							'id'       => $default_id,
							'parent'   => $parent->id,
							'type'     => 'group',
							'children' => array(),
							'meta'     => array(
								'class' => $group_class,
							),
							'title'    => false,
							'href'     => false,
						)
					);
					$default            = $this->_get_node( $default_id );
					$parent->children[] = $default;
				}
				$parent = $default;

				// Groups in groups aren't allowed. Add a special 'container' node.
				// The container will invisibly wrap both groups.
			} elseif ( $parent->type == 'group' && $node->type == 'group' ) {
				$container_id = $parent->id . '-container';
				$container    = $this->_get_node( $container_id );

				// We need to create a container for this group, life is sad.
				if ( ! $container ) {
					// Use _set_node because add_node can be overloaded.
					// Make sure to specify default settings for all properties.
					$this->_set_node(
						array(
							'id'       => $container_id,
							'type'     => 'container',
							'children' => array( $parent ),
							'parent'   => false,
							'title'    => false,
							'href'     => false,
							'meta'     => array(),
						)
					);

					$container = $this->_get_node( $container_id );

					// Link the container node if a grandparent node exists.
					$grandparent = $this->_get_node( $parent->parent );

					if ( $grandparent ) {
						$container->parent = $grandparent->id;

						$index = array_search( $parent, $grandparent->children, true );
						if ( $index === false ) {
							$grandparent->children[] = $container;
						} else {
							array_splice( $grandparent->children, $index, 1, array( $container ) );
						}
					}

					$parent->parent = $container->id;
				}

				$parent = $container;
			}

			// Update the parent ID (it might have changed).
			$node->parent = $parent->id;

			// Add the node to the tree.
			$parent->children[] = $node;
		}

		$root        = $this->_get_node( 'root' );
		$this->bound = true;
		return $root;
	}