Driving myself crazy trying to figure it out. Am a beginner.
Outline your text, draw 2 line to divide it with Object > Path > Divide objects below:
Divide two times, Ungroup, remove the top part. I have moved it aside and colored the mid part to green to show it:
It's a good idea to group the mid part for easy selection. Now it can be distorted. It can be stretched with the direct selection tool by selecting at first the topmost nodes:
Actually this step wasn't necessary, if there's no horizontal parts.
Then make envelope distort, mesh size = 1 x 1
Only one division is needed, if you want to save top parts, but the stretching before envelope distortion is a must to avoid thickening the horizontal parts
Be patient, it takes a while to learn how to manage the mesh points and handles. It's easy to think you would have more control with more complex mesh. For ex. in theory no division is needed, if you have enough rows in the mesh. It's true, but in practice the things become easily unmanageable. Use as simple mesh as possible.