class Main(object):
    def __init__(self):        
        self.db = create_engine('sqlite:///data.db3',convert_unicode=True)
        metadata = BoundMetaData(self.db)
        self.session = create_session()
        self.table = Table('table', metadata, autoload=True)
        self.mapper = mapper(MyClass, self.table)
...
    def addtreeitem(self,event):
        dlg = wx.TextEntryDialog(self, 'Введите имя')
        if dlg.ShowModal() == wx.ID_OK:
            name=dlg.GetValue()
            elem=MyClass(0,name.encode('utf-8'))
            item=self.tree.GetSelection()
            self.tree.GetPyData(item).addchild(elem)
            i=self.tree.AppendItem(item,elem.name.decode('utf-8'),elem.type)
            self.tree.SetPyData(i,elem)
            self.tree.SetItemHasChildren(item)
            elem.save
...
    def refreshtreectrl(self,item):
        self.tree.DeleteChildren(item)
        for el in self.tree.GetPyData(item).children():
            i=self.tree.AppendItem(item,el.name)
            self.tree.SetPyData(i,el)
            if el.haschildren():
                self.tree.SetItemHasChildren(i)
        self.tree.SortChildren(item)
...
class MyClass(object):
    def save(self):
        main.session.save(self)
        main.session.flush
main=Main()

name.encode('utf-8')

name.decode('utf-8')