How to overwrite Startify buffer when open a new buffer in NerdTree

https://user-images.githubusercontent.com/75968004/170257462-811bab36-cb94-4f20-9732-30816ba43804.mp4

In the video, I open NerdTree, then open a file but it didn't overwrite Startify buffer instead open 2 buffers.

How to solve this problem? Thanks in advance.

Start with the linked video and reproduce the interaction between Startify, NerdTree, and opening a file. Trace how buffers are created in this scenario and determine whether the intended result is to replace the Startify buffer; done means the behavior is corrected or clearly documented.

Written by the indexing model from the issue text.