To this day i have never found a telegram group that is specifically about bitcoin, and i am not surprised about it, because bitcoin is already famous and i'm sure many people understand about bitcoin in general
But I am also sure that because when discussing altcoin or trading, usually indirectly we will all discuss bitcoin, which includes price, chart conditions or bitcoin market conditions, so in my opinion there is no need to create a special telegram group that talks about bitcoin.
There are no such bitcoin telegram groups because it is being discussed in some crypto telegram groups about the latest news and updates about bitcoin's price. I don't usually trust some telegram groups because some just unexpectedly invite you to increase the numbers of members to make their group look legitimate and why we need telegram groups if we can feely ask other members here in this forum about bitcoin and other cryptocurrencies.
There are few but sometimes the information you get is not accurate that's why I'd rather prefer to lurk here since there are so many information posted and given by the users compare on telegram where hyping and scamming is so rampant.
You can join for the live discussion of Coinmarketcap via telegram group,(
https://t.me/CoinMarketCap). There are discussions there about exchange and the market movement but it doesn't mean it gives the accurate result of trading and not only exclusive for bitcoin it is generally talking in all crypto.
I don't like to join on any crypto telegram groups but will try to watch the discussion given on cmc channel and let see if they will give a good discussion there
Anyways thank you for the link.