'Helper method to append a child to a node
- Register the parent of the child node
- Append child node to parent children array'

def append_child(self, tnode):

    if (self is tnode):
        raise Exception('Recursive    tree')
    try:
        tnode = tnode()
    except:
        pass
    tnode.parent = self
    bisect.insort(self._children, tnode)
