Wxpython Sizer position

I have the below sample application which has a couple of simple sizers which, for some reason, are centered vertically, which I dont want (see attachment). I want the wxchoice sizer to be position at the top of the window, not in the middle vertically, even when resizing the window, it stays in that position, but I just can't find the asnwer.

import wxclass Mywin(wx.Frame):    def __init__(self, parent, id, title):        super(Mywin, self).__init__(parent, title=title)        self.panel = wx.Panel(self)        self.vbox = wx.BoxSizer(wx.VERTICAL)        nm = wx.StaticBox(self.panel, -1, 'Drop List:')        nmSizer = wx.StaticBoxSizer(nm, wx.VERTICAL)        self.workflowList = ["choice 1", "choice 2"]        nmbox = wx.BoxSizer(wx.HORIZONTAL)        self.workflowChoice = wx.Choice(self.panel, choices=self.workflowList)        self.vbox.Add(nmSizer, 0, wx.ALL | wx.EXPAND, 0)        nmbox.Add(self.workflowChoice, 0, wx.ALL, 5)        nmSizer.Add(nmbox, 0, wx.ALL, 5)        self.btnSizer = wx.BoxSizer(wx.HORIZONTAL)        self.buttonGo = wx.Button(self.panel, -1, "Go")        self.buttonClose = wx.Button(self.panel, -1, "Quit")        self.btnSizer.Add(self.buttonGo, 0, wx.ALL, 5)        self.btnSizer.Add(self.buttonClose, 0, wx.ALL, 5)        self.vbox.Add(nmSizer, 0, wx.ALL | wx.CENTER | wx.TOP, 5)        self.vbox.Add(self.btnSizer, 0, wx.ALL | wx.CENTER, 5)        self.panel.SetSizer(self.vbox)        self.panel.Fit()        self.Show()app = wx.App()Mywin(None, -1, 'Test App ')app.MainLoop()