supply

No.

  

It will be treated as supply if such branches are been registered as two different business verticals....i.e. one separate GST registration for one branch and another separate GST registration for the other branch even in the same state...moreover in many cases branches in the same state is always taken a single registration...and some people does two registration so as to differentiate their business..

If supply of stock transfer is within state then tax is not to be charged. You can transfer stock with following documents:

Delivery challan

E-way bill if value of stock is more than 50,000

However, on interstate branch transfers GST will be charged.