A) Press Ctrl+Up allow keys several times.
B) Right-click just above the Time ruler and drag the mouse up all the way.
C) Hit Ctrl+A (to select all tracks), then drag up the bottom edge of one of the track strips while holding down Shift.
D) Drag up the bottom edge of one of non-active tracks (only when Auto Track Zoom is enabled) -- This is what Craig mentioned.
E) Hit the F key (this collapses the tracks only when there are enough tracks in the Track view).
All available in X2.