wxPython - GetFirstChild() method in wx.TreeCtrl

import wx
class MyTree(wx.TreeCtrl):
    def __init__(self, parent, id, pos, size, style):
        wx.TreeCtrl.__init__(self, parent, id, pos, size, style)
class TreePanel(wx.Panel):
    def __init__(self, parent):
        wx.Panel.__init__(self, parent)
        # create tree control in window
        self.tree = MyTree(self, wx.ID_ANY, wx.DefaultPosition, wx.DefaultSize,
                           wx.TR_HAS_BUTTONS)
        # CREATE TREE ROOT
        self.root = self.tree.AddRoot('root')
        self.tree.SetPyData(self.root, ('key', 'value'))
        # add item to root
        item = self.tree.AppendItem(self.root, "Item")
        item2 = self.tree.AppendItem(self.root, "Item")
        L = self.tree.GetFirstChild(self.root)
        # print tuple of PySwigObject returned from GetFirstChild function
        print(L)
        # expand all nodes of the tree
        self.tree.ExpandAllChildren(item)
        sizer = wx.BoxSizer(wx.VERTICAL)
        sizer.Add(self.tree, 100, wx.EXPAND)
        self.SetSizer(sizer)
class MainFrame(wx.Frame):
    def __init__(self):
        wx.Frame.__init__(self, parent=None, title='TreeCtrl Demo')
        panel = TreePanel(self)
        self.Show()
if __name__ == '__main__':
    app = wx.App(redirect=False)
    frame = MainFrame()
    app.MainLoop()