QListWidget insertItem() Problem

I call the insertItem()  function of QListWidget to insert a data in the first line,But always insert in the last line.

My code is as follows:

AreaSelectUnitWidget* pUnit = new AreaSelectUnitWidget(this);   // new a widget

QListWidgetItem* item = new QListWidgetItem(ui->listWidget);  

ui->listWidget->insertItem(0,item);    // I want to insert it in the first line every time

ui->listWidget->setItemWidget(item,pUnit);    // set widget as item 

When  i call the above code as a function several times，my new inserted widget item always inserted in the last line,not  the first line.

Why doesn't it work?Some people say don't write like that : "new QListWidgetItem(ui->listWidget);", I tried not to use "ui->listWidget" as it parent object,But it still didn't work.Please tell me what should i do?I am a chinese,My english is not good,so please explain it in detail,thanks!