from itertools import chain

class cNode:
    def __init__(self, name = "", attrs = {}):
        self.name  = name
        self.attrs = attrs
                
    def GetAttrs(self):
        return self.attrs.keys()

    def GetValue(self, attr):
        value = None
        try:
            value = self.attrs[attr]
        except KeyError:
            pass

        return value

class cTree:
    class cData:
        def __init__(self, data=None):
            self.child = []
            self.node  = data
        
        def __iter__(self):
            #for nn in self.child:
            #    yield nn
            for n in chain([self], *self.child):
                yield n

    def __init__(self):
        self.data = cTree.cData()

    def __iter__(self):
        for n in self.data:
            if isinstance(n.node, cNode):
                yield n.node
    
    def Append(self, parent, node):
        temp = cTree.cData(node)
        
        if parent is None:
            self.data.child.append(temp)
        else:
            for n in self.data:
                if n.node == parent:
                    n.child.append(temp)
                    break

tree = cTree()
node1 = cNode("root")
node2 = cNode("3")
node3 = cNode("4")
node4 = cNode("5")
node5 = cNode("1")
node6 = cNode("2")
node7 = cNode("10")
node8 = cNode("11")
node9 = cNode("12")

tree.Append(None, node1)
tree.Append(node1, node2)
tree.Append(node2, node3)
tree.Append(node2, node4)
tree.Append(node1, node5)
tree.Append(node1, node6)
tree.Append(node3, node7)
tree.Append(node3, node8)
tree.Append(node3, node9)

for tn in tree:
    print tn.name

root
3
4
10
11
12
5
1
2