1/4″ Reverse Osmosis Filter inlet line to undersink cold water line

I am trying to connect an under counter Reverse Osmosis ( R.O. ) filter inlet line (red 1/4" tubing) to the cold water supply line (3/8" black tubing in picture) under my kitchen sink.

Can anyone help me figure out what sort of Tee/adapter fitting I need to get this done?

Obviously I still need the black cold water supply line to feed the sink faucet as well as this red R.O. Filter inlet line.

I also want the shut-off valve to be in the line to the R.O. filter.

Thanks!

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Additional pictures here showing sizes of connections: https://i.imgur.com/WViRYcs.jpg https://imgur.com/1W8dRrq.jpg https://imgur.com/M18gamH.jpg