It seems like the answer is O(nlogn). I would like to know the steps to figure out this Big O. Thanks in advance!

4. [9 pts] An array of length n (no duplicate items) is to be sorted. Suppose an AVL tree is used to perform the sorting. The sorted result is to be stored in the same array. No other data structure /sorting algorithm may be used. List the steps of the sorting algorithm, and derive (show work!) the big O worst case running time