Extended family tree displays the descendants and/or ancestors from both sides of the family, from father's side extends to mother's side. You can see it as two trees, left half is paternal family tree and right half is maternal family tree. It has two couples in the trunk, they are fatehr's parents and mother's parents. The paternal family includes father's parents, brothers, sisters and their children. Father's father is called paternal grandfather. Father's mother is called paternal grandmother. Father's brother is called paternal uncle. Father's sister is called paternal aunt. The maternal family includes mother's parents, brothers, sisters and their children. Mother's father is called maternal grandfather. Mother's mother is called maternal grandmother. Mother's brother is called maternal uncle. Mother's sister is called maternal aunt. 
 
The two couples are in the trunk, their parents are the ancestry roots, their children (and spouses) are the branches above the trunk, grandchildren (and spouses) are smaller branches, and great-grandchildren are level up to the young twigs and leaves on the end top of the tree.
 
According to Wikipedia, Bilateral descent is a system of family lineage in which the relatives on the mother's side and father's side are equally important for emotional ties or for transfer of property or wealth. So, extended family tree is also called bilateral descent family tree or bilateral kinship family tree, or paternal and maternal family tree.