Assert the page tree shows (or does not show) a page. A path expands the pages before the last one first, so "Congratulations > Features" proves that Features is a subpage of Congratulations. The tree only renders the rows in view, so the step scrolls the tree while it looks.
Examples
Then I should see the "Congratulations" page in the page tree
And I should see the "Congratulations > Features" page in the page tree
Then I should not see the "Congratulations > Checkout" page in the page tree
And we should see the "Congratulations > Content Examples" page in the page tree
Then should not see the "Checkout" page in the page tree
Pattern
Then(/^(I |we )*should( not)* see the "([^"]*)?" page in the page tree$/, …)
Part of @webship-js/typo3-steps (github.com/webship/typo3-steps), a step pack for Webship-js 2.0.x.