How to using Windiff as External Diff in SourceTree
1. Open SourceTree
2. Tools - Options
3. Diff - External Diff Tool : Custom
Diff command : C:\PathToWindiff\WinDiff.Exe
Argument : $LOCAL $REMOTE
*note: put <space> in First letter in Argument
example in command prompt : WinDiff.Exe $LOCAL $REMOTE