If I were choosing a place to sit for 21 days, I would not choose the roots of a tree.
I'd pick a cozy spot, with some straw or hay for cushion.
The hen chose the tree.
For 10 days, she's been depositing eggs in an indentation at the tree's base. Yesterday, she nestled in next to the tree bark. The nearby sapling conceals her, but I know she's there.
I marked the date on the calendar.
In 21 days, we'll see if her choice produces chicks.