I created my first tree a few months ago after determining my birth mother.

Thank you. Congratulations on finding your birth father and creating a new family tree! To answer your question, if you used the same DNA test for both trees, then both trees are connected to your DNA. If you used a different DNA test for your second tree, then you will need to link it to your DNA profile.
To do this, you can follow these steps:

1. Log in to the website where you manage your DNA results and family
   trees.
2. Navigate to the section where you manage your DNA profile or DNA results.
3. Look for an option to link or associate your DNA profile with a family tree.
4. Follow the prompts to link your second family tree to your DNA profile.
   

Please feel free to ask questions if you need additional information! I will be happy to help you out!
There is a better instruction special for you!

1. Log in to your Ancestry account and go to your DNA homepage.
2. Click on "Settings" in the top-right corner of the page.
3. Scroll down to the "Family Tree Linking" section and click "Link to a Tree."
4. Select the tree you want to link from the drop-down menu.
5. Click "Save."