psiTBST (x:xs) = let
        lower = filter (< x) xs
        higher = filter (> x) xs
    in Branch lower x higher
psiTBST (x:xs) = let
        lower = filter (< x) xs
        higher = filter (> x) xs
    in Branch lower x higher
psiTBST (x:xs) = let
        lower = filter (< x) xs
        higher = filter (> x) xs
    in Branch lower x higher