Starting from a list of “tree paths”, for example:

[["a", "b", "c"], ["a", "b", "e"], ["f", "g"]]

I would like to build a forest ([Tree]):

a
|_ b
  |_ c
  |_ e
f
|_ g

This is my attempt so far. I have been constructing the building blocks in order to assemble the final solution:

module Main where

import Data.Tree

insertPath :: Eq a => [a] -> [Tree a] -> [Tree a]
insertPath [] ts = ts
insertPath (y:ys) [] = Node y [] : []
insertPath (y:ys) ((Node x ts):ts')
    | y /= x = Node x ts : insertPath ys ts'
    | otherwise = Node x (insertSubTrees ys ts) : insertPath ys ts'

insertSubTrees :: Eq a => [a] -> [Tree a] -> [Tree a]
insertSubTrees [] ts = ts
insertSubTrees (y:ys) [] = insertSubTrees ys [Node y []]
insertSubTrees (y:ys) (t:ts) = undefined

My questions are:

• Should I define functions over a Tree or a list of Tree ?
• Is my approach sensible ? What are other alternatives ?
• How can I develop a buildForest :: Eq a => [a] -> [Tree a] -> [Tree a] function ?