Why trimethylamine si pyramidal but trisiluylamine is planar ?

Trimethylamine is a pyramidal molecule and formamide is a planar molecule the hybridisation of Nitrogen in both is

Trimethylamine oxide is excreted in

Trimethylamine is less basic than dimethylamine.

Trimethylamine is a stronger base than trisilylamine. Justify.

In aqueous solution, trimethylamine is more basic than methylamine.

In aqueous solution, trimethylamine is more basic than methylamine.