In order to manage Blog Category Tree in Magento 2 Blog, please go to the Admin Panel > Stores  > Configuration  > Magefan Extensions  > Blog > Sidebar and find Categories Widget section.

Categories Widget

1. Enable or Disable the widget.

2. Enable the Display Number Of Posts, if you want the number of posts to be displayed near the category link.

3. Maximum Depth defines the layers number of categories and subcategories that will be shown in the Category Tree. (e.g. if you set it to 2, except for the root category "Fashion" there will be shown "Fashion show" subcategory)

4. Set the Sort Order to manage the position of the widget on the StorefrontThe higher the number of the position, the lower it will be displayed on the Sidebar.

Once you've finished don't forget to Save Config and Flush Magento Cache.

Magento 2 blog category tree configuration

5.  Check the blog Category Tree out on the storefront.

Magento 2 blog category tree