This tree is created collapsed
You can click the top categories.
Collapse all -- Collapse the whole tree and show only the top branches
Expand all -- Expand the tree and show all the branches.
Toggle lines -- Hide/display the lines that connect the various nodes.
Open "World" -- Open to the branch that includes the "French" node
Open to "Recreation" -- Open to the branch that includes the "Travel" node

You can associate callbacks with users' node clicks.
Here we just display the node, but you can customize the code to perform other actions in response to node clicks.