Getting unknown property: common\models\db\Category::depth

[russeljo]

Extension ask for depth property, but no words in readme about it
vendor\koperdog\yii2-treeview\base\TreeHelper.php at line 66– yii\db\BaseActiveRecord::__get()

for ($depth = $models[0]->depth; $n->depth > $depth; $depth++) {
       $node = &$node[count($node) - 1]->children;
}

in view i use

<?= TreeView::widget([
    'emptyText' => 'Nothing found',
    'layout' => "{items}\n{pager}",
    'dataProvider' => $dataProvider,
    'filterModel' => $searchModel,
    'tableOptions' => ['class' => 'table table-bordered table-hover dataTable'],
    'columns'      => [
        Category::ATTR_NAME,
        Category::ATTR_SLUG,
        [
            'label' => 'Parent category',
            'attribute' => Category::ATTR_PARENT_ID,
            'value' => 'parent.name'
        ],
        [
            'class' => 'yii\grid\ActionColumn',
            'template' => '{update} {delete}',
            'buttons' => [
                'update' => function ($url) {
                    return Html::a(
                        '<i class="fa fa-pencil" aria-hidden="true"></i>',
                        $url,
                        [
                            'title' => 'edit',
                            'class' => 'btn btn-primary'
                        ]
                    );
                },
                'delete' => function ($url) {
                    return Html::a(
                        '<i class="fa fa-trash" aria-hidden="true"></i>',
                        $url,
                        [
                            'title' => 'delete',
                            'class' => 'btn btn-danger',
                            'data-confirm' => 'confirm action',
                            'data-method' => 'POST',
                        ]
                    );
                },
            ],
        ],
    ]
]) ?>

Explain, please, data structure. How it idetify parents and childrens?