I will summarize for you the main parts of a tree and their function. This should help you come up with similarities (transport; growing) and differences (what is their specific task).

The main parts of a tree are:
The roots,
The stem, trunk and branches
The leaves

Roots:
Roots anchor the tree to the soil and hold it firmly in the ground. They may grow primarily down and sideways. Roots may not go down deep but they can spread outward as far as the tree is tall. Some trees have deep tap roots, others have a spreading system of roots. Roots also take in water and other nutrients like nitrogen, phosphorous, potassium, calcium, sulfur and magnesium which the tree will need to live and grow.

Stems, Trunks and Branches:
The stem of a young tree plant will become its trunk and branches. The job of the trunk and branches is to support, protect and transport. The trunk and branches hold up the leaves, flowers and fruit of flowering trees. They grow primarily up and out. On the outside of the trunk is the bark. It protects the tree from extreme temperatures, bad weather, insects and fungi. Inside the trunk and branches are two groups of pipes. One group of pipes carries water and nutrients from the roots to the leaves. The other group of pipes carries the food made by the leaves to the other parts of the tree.

Here's a look at a tree trunk from the inside to the outside and a description of what each layer does:
Heartwood - inner core of dead wood that supports the tree. Sapwood (xylem tubes, part of inner bark)- the youngest layer of wood that transports water and minerals up the tree. Cambium (part of inner bark) the growing layer that is only one-two cells thick. It makes new cells during the growing season that become part of the phloem, part of the xylem, or more cambium. Phloem (part of inner bark) - the food supply line that carries sap (water containing dissolved nutrients and sugar) from leaves to branches, trunk, and roots and in the spring brings the sap back up to the tree parts. Outer Bark - protects the tree from injury and disease.

Leaves: Leaves provide trees with all their food because they turn sunlight into food energy in a process called photosynthesis.

Chlorophyll, a pigment in the leaves, is capturing light energy and makes this energy transformation possible. Leaves also make the oxygen in the air that we breathe. Sunlight shines through the top of the leaf and reaches the next layer of cells. The light energy is trapped by the chlorophyll in the chloroplasts. In the chloroplasts, a process that uses water changes the light energy into a kind of chemical energy. This chemical energy is stored in the chloroplasts.

The chloroplasts use the chemical energy to make food. Air enters the leaf through the stomata and moves into tiny spaces around the food-making cells in the leaf. Carbon dioxide from the air passes through the cell walls and membranes of the cells. Carbon dioxide enters the chloroplasts where the previously stored chemical energy converts the carbon dioxide into sugar.

Tubes in the plant carry sugar from the leaf cells to other parts of the plant, such as roots, stems, and fruits. Cells in these parts of the tree store some of the sugar.

You can learn more about trees here.