Create a binary tree, code review request
I only see one really questionable thing in your code.  Why do you call this() in your constructor?  Your parameter-less constructor does absolutely nothing, so this line is irrelevant.  If anything, I would actually even remove that constructor entirely so that your API can only be used with your meaningful and useful one.

Also, as a side note, the following line opens you up to a NullPointerException since you never check to see if items is null or if it has any elements.

root = new TreeNode(null, items.get(0), null);