I am a little confused with confirmation mechanism in bitcoin PoW consensus.
According to bitcoin wiki:
After a transaction is broadcast to the Bitcoin network, it may be included in a block that is published to the network. When that happens it is said that the transaction has been mined at a depth of 1 block. With each subsequent block that is found, the number of blocks deep is increased by one. To be secure against double spending, a transaction should not be considered as confirmed until it is a certain number of blocks deep.
Let's say if A has 1 btc, and A sent 1 btc to B as transaction T1 and also sent 1 btc to C as transaction T2. It is possible that these 2 transactions are written into 2 different branches.
In this scenario, if miner M1 keeps mining based on branch with T1 and M2 keeps mining based on branch with T2, finally subsequent block for these 2 branches will more than 6, and in most of apps these 2 transactions will be regarded as legal. I am thinking there might be other verification to make a block regarded as confirmed.
My question is: what makes a transaction confirmed? Thanks in advance.