1. 

A tree is a data structure where data is stored in nodes. Nodes are arranged in branches where each node can expand into 0, 1, or 2 other nodes.

2. 

A parent node is a node that branches into one or two other nodes, which are called child nodes.

3. 

A key is a component of a node that identifies the node. An application searches keys to locate a desired node. A value is also a component of a node that is used to store data.

4. 

A root node is another term for a parent node.

5. 

The left child node has a key that is less than the key of its parent node. The right child node has a key that is greater than the key of its parent node.

6. 

A leaf node is the last node on a branch and does not have any child nodes.

7. 

The depth of a tree is the number of levels of a tree.

8. 

The size of a tree is the number of nodes on the tree.

9. 

You calculate the size of a tree by using the following formula:

size » 2 ^depth

If the depth is 5 levels, then the size is 32, as shown here:

32 » 2 ⁵

10. 

No, a tree cannot have a duplicate key.