How to implement a binary decision tree on google actions using dialogflow fulfillment node.js?

I want to ask the users a few questions in my welcome intent and depending on their answers give them a particular output.
My problem is that, once the user answers the first question, the agent exits my welcome intent and tries to match with the next intent.
I thought I could solve this by matching it back to the welcome intent.
So ideally it should have gone like this :
Welcome intent -> 1st question -> user answer -> Welcome intent ->2nd question -> and so on
But actually this happens :
Welcome intent -> 1st question -> user answer ->Welcome intent -> 1st question
It will keep asking the first question.
To solve this , I started maintaining a flag for each question.
If question 1 was answered I would set its flag true and then use it to skip the first question when the welcome intent is matched for the second time.
This is a very convoluted way to do it and probably far from the best way to do it.
Can anyone point me in the right direction to implement it?
Thank you.

Edit : I have given up my old method. Let me explain what I want to do and then I can get guidance on the way I should implement it.
I have 16 different outputs and I would like to show one of them to the user depending on their answer to 4 questions. Each question will only have two answers as options and depending on the option chosen by the user for each question , I will pick one of the 16 outputs and display it to the user.
How do I accomplish this using diaglogflow node.js?

First of all remember that an Intent captures what the user says or does and not what you do with that information or how you reply to it. That part is best handled by your fulfillment. While we can use Contexts to limit which Intents will be considered for a user response they are probably most useful in this case to store your state and keep track of which questions have been asked and answered.

Under this scheme, your Intents remain responsible for capturing input and your fulfillment examines this input, changes state based on this input, and sends a reply based on the new state (what it needs to ask next). If the user's responses will be mostly the same (free form, or from the same set of phrases), you can even use the same Intent to capture this input and the fulfillment would use the state and input to determine what logic to execute. If you need different types of input, and thus different Intents, their handlers can still call common functions to do the processing and change the state/reply.

This is further discussed in Thinking for Code: Design conversations not logic

You can use the concept of the follow-up intents in Dialogflow Console to create a chain of questions/answers.

Here is an example of my chain of questions/answers:

Though I still strongly advise you to study also how input/output context works. Especially if you want to collect all user reply parameters in the one final fulfillment of the last step to avoid storing the user inputs in fulfillments attached to every intent of the chain.