I've been given several tasks, and each task should be pushed it its own branches. For example, task_1 files into task_1 branch. I've created branches from task_1 to task_8 for each task. 
However, before working on a specific task, let's say task_3, I created a new branch for task_3 by git branch -M task_3. Then, I created a folder named task_3 and kept all files related to the task there. Having finished the task, I did: git add task_3 and git commit -m "task 3 finished" and git push origin task_3. 
The funny thing is all the previous commits (task_1 and task_2) were pushed to task_3 branch. For example, in task_8 branch, all the previous commits were also pushed to task_8 however I added only task_8 folder to the staging area then made a commit and push. 
Is there any way to ignore previous branches and commits when pushing files to each lastly created branch?
The repo is here.
Also, I am asked to create a pull request on each branch and files should be added to the main branch before merging. How am I supposed to do that? 
I appreciate your help.
