growing trees

Greetings,

For my own edification I have written a few functions for creating a
tree from a list of 'associations'.
An association is defined as

data Assoc = Assoc { label :: String
                   , assocId :: Int
                   , assocPid :: Int
                   }
                   deriving ( Show )

where assocId is an int that uniquely identifies a node, and assocPid
is the id of that node's parent.

The idea is to feed an array of these associations into a function and
get a Data.Tree Assoc out.

So I have code that does the job ...  ... but it's not very good.  I
thought the problem might be
solved with a fold, but that proved difficult due to the Assocs not
being in a suitable insertion order.

Perhaps the routines can be improved such that the array order doesn't matter.

Any advice, or better versions would be appreciated.

thanks,
Jeff