If you have a step in your tree where you want to verify the end-user performed an action, you can use the "Require Confirmation" feature when editing a node.

When the end-user is in the tree, they will see a message in red ink like this:

The buttons will remain deactivated until the user ticks the checkbox.

Here's how to set this up:

1. Edit the node that you want to contain this message.
2. In the Question and Action Buttons section add at least one button.
3. Check the Require a confirmation click to activate buttons option.
4. Enter a message to display to the end user. It will look like this in the editor: