Is there a regular tree language in which the average height of a tree of size $n$ is neither $\Theta(n)$ nor $\Theta(\sqrt{n})$? We define a regular tree language as in the book TATA: It is the set of trees accepted by a non-deterministic finite tree automaton (Chapter 1) or, equivalently, the set of trees generated by a regular tree grammar (Chapter 2). Both formalisms hold close resemblances to the well-known string analogues.


  Is there a regular tree language in which the average height of a tree of size $n$ is neither $\Theta(n)$ nor $\Theta(\sqrt{n})$?


Obviously there are tree languages such that the height of a tree is linear in its size; and in the book Analytic Combinatorics it is shown e.g. that binary trees of size $n$ have average height $2\sqrt{ \pi n}$. If I understand Proposition VII.16 (p.537) of the mentioned book correctly, then there is a wide subset of regular tree languages that have average height of $\Theta(\sqrt{n})$, namely those in which the tree language is also a simple variety of trees fulfilling some extra conditions.

So I was wondering whether there is a regular tree language showing a different average height or if there is a true dichotomy for regular tree languages.

Note: This question has been asked before on Computer Science, yet it has been unanswered for more than three months. I would like to repost it here because the question is too old to migrate and because there is still an interest in the question. Here is a link to the original post.
I believe that the answer is as you suggest that no other asymptotics than $\Theta(1)$, $\Theta(\sqrt{n})$ and $\Theta(n)$ are possible. A promising route to prove this could be to apply the techniques from the paper which derives the $\Theta(\sqrt{n})$ asymptotics to the run trees of the regular language. Notice that a tree is accepted if there exists a run tree so it should be possible to first derive (using loc.cit.) the average height of a randomly generated run tree and take it from there, i.e. show that projecting away the states does not change the average height.