Dependency tree doesn't give versions-maven-plugin source

Question

I am using below command to identify versions-maven-plugin source, since the specified plugin has not been directly defined in the project. But it doesn't show any details related to the said plugin.

mvn dependency:tree

However below command gives the plugin info

mvn -Dplugin=org.codehaus.mojo:versions-maven-plugin help:describe

Results:

Name: Versions Maven Plugin
Description: The Versions Maven Plugin is used when you want to manage the
  versions of artifacts in a project's POM.
Group Id: org.codehaus.mojo
Artifact Id: versions-maven-plugin
Version: 2.14.1
Goal Prefix: versions

Further I was trying to override the version by adding below into the project main pom. However same previous version (i.e. 2.14.1) shows plugin describe results.

    <build>
        <pluginManagement>
            <plugins>
                <plugin>
                    <groupId>org.codehaus.mojo</groupId>
                    <artifactId>versions-maven-plugin</artifactId>
                    <version>2.13.0</version>
                </plugin>
            </plugins>
        </pluginManagement>
        <plugins>
...