(Using Blender 3.6.8)
With Trim Curve nodes, the Bezier curve is split in 3 splines using the Factor parameter to define the endpoint positions.
Start: (see top branch of the following graph) The position of the second control point (i.e. with Index equal to 1) is recovered with a Sample Index node set in Point domain. Then the spline made of the first and second control points is subdivided once.
End: (see bottom branch of the following graph) The index of the before last control point is computed from the Point Count returned by a Domain Size node set in Curve domain, by subtracting 2 (because Index starts at 0). Once its position is recovered, the spline made of the before last control point and of the last control point is subdivided.
In between both: (see central branch of the following graph) The spline made of all control points between the second one and the before last one (included) is unmodified.
Resources: 