ORDER BY with LTREE

Hello!

Im working with the ltree [1] datatype and have labels that can not used
directly in ltree and a want to get a tree like strukture ordered by the 
labels.

IE, I've got a table

CREATE TABLE t
(tree     LTREE,label    TEXT
);

and data like

tree        label
--------------------------
root.1        z
root.2        c
root.2.1    a
root.2.2    b
root.3        i
root.4        f
root.4.1    k
root.4.2    c

I need a VIEW that ordery by "by tree but by label in the same hirachie", 
so the output should be

root.2        c
root.2.1     a
root.2.2     b
root.4        f
root.4.2     c
root.4.1     k
root.3        i
root.1        z

Any idea?

Thanks, 
AXEL.
[1] http://www.sai.msu.su/~megera/postgres/gist/ltree/