Clean the tree and view parameters

def initialize_view(self):
        """Clean the tree and view parameters"""
        self.clear()
        self.item_depth = 0   # To be use for collapsing/expanding one level
        self.item_list = []  # To be use for collapsing/expanding one level
        self.items_to_be_shown = {}
        self.current_view_depth = 0