What is Wavelet packet transform (WPT) time complexity I have read in many papers that time complexity of WPT is $O(N \log(N))$, but I would like to know what is the effect of Levels in the time complexity. 

Must it be one of the following ?


$O(2^{L} ~N~ \log(N))$  
$O(2^{L+1} ~N~ \log(N))$ 
$O(L ~N ~\log(N))$


$ L$ is the number of decomposition levels

Can anyone helps which is true?
I just found the answer in a paper. so thought it might be useful for someone.
If we decompose a signal with length of $N$ to $L$ level then time complexity is
$O(L\times Nlog_{2}N)$