Bitbucket pipelines docker image with multiple FROM? [duplicate]

Question

First of all, I'm brand new to Docker! I am currently trying to create my own docker image which I can use in my bitbucket pipelines. What I am trying to do is install node and ruby on the same container. Here is what my current Dockerfile looks like:

FROM node:12.22.10

FROM ruby:2.7.5

I've built, tagged and pushed this image and use it in my bitbucket-pipelines.yml and I'm trying to run this step script:

script:
    - yarn install
    - gem install bundler -v 2.2.29

When this is run in the pipeline I get this error:

bash: yarn: command not found

I've tried a couple of things, I removed the FROM ruby:2.7.5 and the yarn command worked but obviously the gem install bundler... did not. So, I know that the Dockerfile and image are working but I don't know how to use both images in my own Dockerfile. Does anyone know what I'm doing wrong?