A note on the terminology that I try to use – others may use the same terms in different ways.
Sometimes you find a record of an event that refers to one person, such as a burial or a person alone on the census with no relatives co-resident. That’s an unconnected event, until I find the right person to attach it to.
The family group is the basis of family history – sounds obvious! You can find a family on the census – head, wife, sons and daughters. You find families in baptism records – “Elizabeth was baptised to John and Mary”. So I use the term family group for just that – father, mother and children – in other words, 2 generations. When you look at the families, you can start to attach other events to the people in the families.
If 2 family groups can be linked, then that creates a small branch – we now have 3 or more generations. This linking is the basis of the reconstruction that I do, trying to link all families into branches. I now have about 40 branches, 15 going back from the present day into history; 14 have died out before reaching the present; another dozen or so go back from the present day for 50 to 100 years but I have not been able to link them into the other branches.
A tree could be considered to be a big branch. However I tend to reserve trees for related branches – we know from DNA tests that 2 large branches are related – so that’s a tree to me! We have 3 DNA haplogroups, so 3 trees.
Well, that’s how I try to use the terms – I don’t always achieve consistency!
Andy Micklethwaite's Family History Blog 