QTreeWidget ui was not declared

hey this is my code and It says that 'ui' was not declared

Dialog::Dialog(QWidget *parent) :
QDialog(parent),
ui(new Ui::Dialog)
{
ui->setupUi(this);

ui->treeWidget->setColumnCount(2); //and it says there is a problem there too about ->treeWidget must point to class/struct/pointer
AddRoot("hello", "world");
}

Dialog::~Dialog()
{
delete ui;
}


void AddRoot(QString name, QString description)
{
QTreeWidgetItem *itm = new QTreeWidgetItem (ui->treeWidget);

itm->setText(0, name);
itm->setText(1, description);
ui->treeWidget->addTopLevelItem(itm);

}

Did you add a QTreeWidget class instance into your Dialog.ui file named "treeWidget" when you used Qt Designer to define your dialog's UI?

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