A perfectly legitimate party, the Scottish National Party (the clue is in the name) put seeking Indepence for Scotland in their manifesto in 2007.
At the 2011 Scottish election, the SNP won the election, so they had a mandate for the Scottish people to seek Indepenence.
The British Government insisted on a referendum to clarify that Independence is what the majority of Scots want.
Salmond as leader of the SNP and of the Scottish Assembly is entirely within his rights to take this course. It is not one man leading this, he is leader of a Party with many members, who could get rid of him if he was not doing what they wanted. And he is leader of the Scottish Parliament, fairly elected.
No it is not treason. Presumably you mean to the Queen. In all probability the Scots will retain the Queen just as Canada and Australia do. They will be a member of her Commonwealth. Which is why HMQ is staying out of the Yes/No debate. She is looking at the longer picture.