A tree consists of roots, a trunk and a crown.
The crown itself consists of many branches, bigger and smaller one.
The biggest branches are connected to the trunk.
They split into smaller branches, which again split into small ones.
Finally the leafs grow out of the smallest branches.
You find a very similar structure by the roots.
They grow from the trunk into the soil and have the purpose to anchor the tree in the ground and also for gathering water and nutrients from the soil.
The master roots are connected directly the the trunk and parts of this roots are still above the soil.
They split up into smaller ones and you get a structure that is in some kind similar to the structure of blood vessels.