SET EXTERNAL DIFF TOOL ON SOURCETREE
There is a way to check the differences in external tool in sourcetree. The below are the steps to enable your favourite code compare tool.
Menu Tools -> Options,
Previously the External Diff Tool is SystemDefault by default. You can select any of your favourite tool in the Combo list
After set the external diff tool, you can see the differences in your tool. I have selected BeyondCompare tool. On click of External Diff popup menu, you will get the differences in your favourite diff tool.