You can automate the MIDI clip itself using the clip viewer. Double-click on the midi clip. Next, select the Show/Hide Envelope Box button at the bottom left of the clip viewer (remember the names and functions of each button will appear in the help box to the left of the DAW when you hover the mouse icon over them). From there, select 'volume' from the 'Control Chooser' drop-down menu. Go ahead and automate using breakpoints, as shown in this tutorial.  Note: You cannot use this technique to fade in the track itself, only MIDI clips within that track. Also, note that your MIDIi clip's volume will be affected twice if you automate the clip using the clip viewer and any gain automation you do on the track itself using the Utility plugin.