Use case: I like to be able to show the dependency tree for my sbt projects, so I have added `addDependencyTreePlugin` to my `~/.sbt/1.0/plugins.sbt`, to make it globally available on my machine.

However, that plugin is only available since sbt 1.4.x (not sure about the exact version).

Problem: whenever I try to build a project that has an `sbt.version=1.3.x` or lower in the `build.properties`, it will fail.

Is there a way to conditionally do the `addDependencyTreePlugin`, based on the 'current' version of sbt that is being used by the build process?

This does not work:

```
addDependencyTreePlugin.filter(es => sbtVersion.value.startsWith("1.5")

```

sbt will complain about:

```
.../plugins.sbt:4: error: `value` can only be used within a task or setting macro, such as :=, +=, ++=, Def.task, or Def.setting.
addDependencyTreePlugin.filter(es => sbtVersion.value.startsWith("1.5"))
^

```