What is that forge error message?

I installed a few mods via the Twitch Launcher. But if I want to start Minecraft is there (crash). Here is the error in the log file:

Since you have probably messed up with different versions, or just had bad luck.

Duplicate method name & signature in class file net / minecraft / block / BlockLeavesBase

The loading of the BlockLeavesBase works net. Install the version again

Thank you.