On click of row how to dynamically add subrows in SKSTableview

[sakshigidwani93]

In didSelectRowAtIndexPath, i want to dynamically subrows but this code is not working.

This is my array
_arr_Alphabets = [[NSMutableArray alloc] initWithObjects:
@[
@[@"A",@"A1",@"A2"],
@[@"B", @"B1",@"B2"],
@[@"C", @"C1",@"C2"],
], nil];
trying to insert object a3 after a2
[[[_arr_Alphabets objectAtIndex:0] objectAtIndex:0] insertObject:@"A3" atIndex:3];

error unrecognized selector sent to instance