There is a method Right() in the RB tree implementation:

public int Right(int node)
{
  return items[node].right;
}

JIT does not want to inline it, probably as the method may throw:

public int Right(int node)
{
  return items[node].right;
00000000 mov eax,dword ptr [ecx+4]
00000003 cmp edx,dword ptr [eax+4]
00000006 jae 00000013
00000008 shl edx,4
0000000b lea eax,[eax+edx+8]
0000000f mov eax,dword ptr [eax+8]
00000012 ret
00000013 call 74C3A62C
00000018 int 3

Too sad.