code:

leaves :: [Node]
leaves = concat leafPairs
    where
        valuePairs = chunksOf 2 [1..2^k]                   -- I can trace this
        parentValues = map sum valuePairs                  -- and this
        parents = getParents $ zip parentValues leafPairs  -- but not this
        leafPairs = zipWith build parents valuePairs       -- or this
        build parent [valueA, valueB] = [Node valueA r, Node valueB r]
            where r = Leaf $ Parent parent


-- We're down to one parent, so make it a root
getParents :: [(Integer, [Node])] -> [Node]
getParents [(value, [childA, childB])] = [Node value $ Root children]
    where children = Children childA childB