Add an icon to a Qtreeview item in python and without using the QstandartItemnModel

I would like to add an icon for each item in my QTreeView. The problem is : I am not sublassing my QTreeView from QStandartItemModel but from QAbstractItemModel so I don't have access to the set_icon method.

Here is the function I've done :

def set_icon(self,column : int , icon :QIcon) :
        if column < 0 or column >= len(self.item_data) :
            return False
        self.icon = icon
        self.item_data[column] = self.icon
        return True

I copied this method from the set_data method that is found in the treeitem.py, I thought it would work the same way. Then, when I populate my QTreeView, I wrote this line so it should add an icon to the second column of the line :

child.set_icon(1,QIcon(":/Icons/C:/Users/E40055301/Desktop/Icones/mail.svg").pixmap(QSize()))

I don't have any error message, but the Icon doesn't show, so I tried to write it in many ways but none is working.

You need to return the icon in the data() method for the DecorationRole.

def data(self, index: QModelIndex, role: int = None):
    if not index.isValid():
        return None
    
    if role not in (0, 1, 2):  # using the enum values instead of names
        return None

    item: TreeItem = self.get_item(index)
    value = item.data(index.column())

    if role == Qt.DisplayRole or role == Qt.EditRole:
        return value

    if role == Qt.DecorationRole:
        if value == 1:
            return QIcon('path_to_icon_1.jpg')
        if value == 2:
            return QIcon('path_to_icon_1.jpg')