Not sure what you are asking/ A tall twin mattress will not fit in a standard trundle.You might be able to have something made but I can’t imagine it would fit under your bed without being smaller.

I had one of these in my spare room, it is adjustable.

https://www.amazon.com/Hillsdale-Furniture-90010-Pop-Trundle/dp/B000G1YF4A/ref=asc_df_B000G1YF4A/?tag=hyprod-20&linkCode=df0&hvadid=295625933267&hvpos=1o2&hvnetw=g&hvrand=1561316134746344861&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9015072&hvtargid=pla-570384324144&psc=1

Patricia, I’m wanting to place a tall twin under a tall twin . I want a pop up trundle that accommodates the tall twin on the bottom . The only trundle beds I’ve found are for regular twin. Guess it’s a missed opp. for the manufacturer. I’ll see what my sons can build. It’s not that an unusual request.

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By tall twin, do you mean an XL extra long twin mattress? Did you look at the link suedomin75 posted? The frame is 72" long and it looks like it is designed for the top and bottom of the mattress to overhang the frame a little. Seems like an XL twin mattress would just overhang a few inches more.