To export specific branches of your family tree:
Open your tree in Family Tree Builder.
Go to File > Export GEDCOM.
Click Save As, choose the folder on your computer you’d like to save to and click Next. In your case, you will want to give this tree a different name than your main tree. You may want to name it after the eldest ancestor in the branch you are exporting, for example.
If you wish to fill in author information or add a description to the file, you can do so here. It is not necessary though. Click Next.
Choose the language of the tree. Click Next.
This is the screen where you will choose a specific branch to export. Choose the “Include specific people only” option and click Select People.
Click Add to select people from your tree. I suggest you review your family tree before completing these steps and choose which ancestral branches to export. It will save you a lot of time when you get to this step.
Select the person you want to add. (In the next step you will choose if to include descendants, so select only the eldest ancestors).
For each person you choose, you can include Descendants and Spouses, Descendants only, Spouses only, or only This person. Use the Edit button to do this. When you’re finished click OK.
If you have photos in the tree, you’ll see the above screen. It is recommended to click Yes.
Click Finish. You have just created a new tree which contains a certain branch of your family only. **Exporting a branch from the family tree has no effect on the main tree.
In order to publish this tree, you will want to open it in Family Tree Builder first. Go to File > Import GEDCOM and import the GEDCOM you just created. Then publish it to your family site.