Uri(Uri, String) constructor does not works properly?

Uri(Uri, String) constructor does not works properly?

Here is a part of my code:
Uri branches = new
Uri(@"https://127.0.0.1:8443/svn/CXB1/Validation/branches");
Uri testBranch = new Uri(branches, "test");
I expect testBranches will be
https://127.0.0.1:8443/svn/CXB1/Validation/branches/test, but it is
https://127.0.0.1:8443/svn/CXB1/Validation/test. I can not understand why
Uri(Uri, string) constructor eats the last part of the path.