glGo offers a tree display to get a visualization of the variations in a game, much similar to the tree in CGoban2, which I personally consider the best tree available, but that's a matter of taste. To open the tree window, select in the boards menu. glGo will remember this setting and always show the tree if you open the SGF editor. However, it will never show the tree by default for IGS or GNU Go games, but you can still open the tree manually. I assume the tree is not too interesting for real games. glGo will also remember the size and position of the tree window.
The tree supports folding and move navigation. The most obvious way to access these action is by right-clicking on a node to open a popup menu. The popup will display the available actions. If you right-click on some empty space in the tree window, the popup will display global configuration options instead of the actions associated with one node. Currently there is only one global option available: You can select a different background color.
You can perform the same actions in the popup menu by clicking on nodes or the intersections. This should be more convenient to use.
Click on a node to navigate to this move.
Click on a horizontal connector (the blue line) between two nodes to fold or unfold.
Click on a connector between a node and its branches will fold or unfold all branches after their first move (so you keep seeing the start of the variation)
Double-click on a connector between a node and its branches will completely hide or show all variations.
If a branch is folded, the tree will still display the blue connector line, so you can see where folded moves are available. If you hide all variations of a node, it will draw a small vertical connector line to indicate this node has branches.
When adding moves or navigating in the board, the tree will automatically scroll to the correct position.