Creating a simple `FWTreeView` instance

The FWTreeView module lets you load nodes on the fly, you just need to provide a function that will be called whenever a node is expanded the first time.

In the example below, we create a simple, shallow tree with three initial nodes, using the `tree` property in the configuration object. In that same object we set the dynamic loader.

The dynamic loader function receives two arguments, the node being expanded and a callback. The dynamic loader uses the information of the node to fetch its children, usually some value that can be used in a remote request to a server. In this case, we simply use the label of the node being expanded to produce the labels of the child nodes by appending an index to each label.

For most nodes, a simple string is all that is needed to define a node. That string is used as the label for each node. To set other options, an object must be provided. For each set of nodes added to each branch, a last, childless node is added. To signal that the node have no children, the `isLeaf` property must be set, otherwise, FWTreeView assumes all nodes can be expanded. Note the lack of a toggle icon on the last node of each new branch.

Once the array of new nodes has been obtained, the callback must be called with the array as its single argument.

The dynamic loader has a one second delay to simulate the delay that might occur when requesting data from a remote source.