C# code to create Terms and Term Set programmatically (using code)?

Add reference of "Microsoft.SharePoint.Taxonomy" assembly to your project. Include namespace "Microsoft.SharePoint.Taxonomy". And use the code as listed below.

 using (SPSite site = new SPSite("Site URL"))

            {

                TaxonomySession _TaxonomySession = new TaxonomySession(site);

                //Get instance of the Term Store 

                TermStore _TermStore = _TaxonomySession.TermStores["My Term Store"];

                //Now create a new Term Group

                Group _Group = _TermStore.CreateGroup("My New Group");

                //Create a new Term Set in the new Group

                TermSet _TermSet = _Group.CreateTermSet("My New Termset");

                //Add terms to the term set

                Term _term1 = _TermSet.CreateTerm("First Term", 1033);

                Term _term2 = _TermSet.CreateTerm("Second Term", 1033);

                Term _term3 = _TermSet.CreateTerm("Third Term", 1033);

                Term _term4 = _TermSet.CreateTerm("Last Term", 1033);

                //commit changes

                _TermStore.CommitAll();

            }