How can i merge new development branch to existing branch with conflict file.

[Ranjithkumar]

I clone the code from master branch and named as existing branch.Now i again clone the code from existing branch and named as new branch.I develop existing branch and new branch parallely.Now i can not merge new branch to existing branch due to some conflicts file is there.how can i move it to existing branch with the help of source tree tool.I am using bit bucket and source tree.