I can no longer boot into macOS after resizing my bootcamp partition The Problem: My macOS partition doesn't appear as an option at boot
Background: I had a main el capitan partition and a bootcamp partition. I used the EaseUS program to resize the bootcamp partition from 90GB to 45GB and after rebooting, I could no longer see any option but 'Windows' when holding alt at boot.
My Initial Investigation:  I took a look at my paritions in three different places: The EaseUS program, diskpart on windows, and the disk utility on macOS Recovery Mode.
On both EaseUS and diskpart, my partitions look fine:


However, in disk utility in recovery mode, it looks a bit different. On the sidebar I can only see one child partition of the SSD (BOOTCAMP). However when inspecting the disk, it shows three partitions (Untitled : 145.36GB, Untitled: 650MB, BOOTCAMP: 48.32GB) and a 'Child count' of 4. I wish I could provide a screen shot, but AFAIK this is not possible with recovery mode.
I also ran first aid on the SSD from disk utility and everything verified as OK.
Additional Comments: I'm a bit out of my depth here  and would really appreciate any advice as to how I can boot into macOS again
Edit #1:
In response to @DavidAnderson
I am using a an early 2015 13&quot; Retina MacbookPro (MacbookPro 12,1).
My Volume 2 details are as following:
Partition 2
Type    : de94bba4-06d1-4d40-a16a-bfd50179d6ac
Hidden  : Yes
Required: No
Attrib  : 0000000000000000
Offset in Bytes: 209735680

  Volume ###  Ltr  Label        Fs     Type        Size     Status     Info
  ----------  ---  -----------  -----  ----------  -------  ---------  --------
* Volume 2         Macintosh H  HFS    Partition    135 GB  Healthy    Hidden

And my volume 3 details are:
Partition 3
Type    : de94bba4-06d1-4d40-a16a-bfd50179d6ac
Hidden  : Yes
Required: No
Attrib  : 0000000000000000
Offset in Bytes: 145570975744

  Volume ###  Ltr  Label        Fs     Type        Size     Status     Info
  ----------  ---  -----------  -----  ----------  -------  ---------  --------
* Volume 3         Recovery HD  HFS    Partition    619 MB  Healthy    Hidden

Edit #2:
I was able to fix it with the accepted answer!
I used gdisk and the t command to set the GUIDs as recommended and then used the the expert command a (expert commands are accessed with x) to set the attribute field #49 to get the attribute value recommended. Works perfectly now!
Your second partition should have GUID (Type) of 48465300-0000-11AA-AA11-00306543ECAC. The third partition should have a GUID (Type) of 426F6F74-0000-11AA-AA11-00306543ECAC and an attribute (Attib) value of 0002000000000000. You will need to correct these values.

A good third party tool used to edit the GPT is gdisk.

Once downloaded, you invoke the command by entering the following in an Administrator Command Prompt window.

gdisk64 \\.\PhysicalDrive0


The command gdisk abbreviates the GUID values. Below are some of the abbreviations. 

GUID                                  Abbreviation  
------------------------------------  ------------                       
48465300-0000-11AA-AA11-00306543ECAC     AF00
426F6F74-0000-11AA-AA11-00306543ECAC     AB00 
DE94BBA4-06D1-4D40-A16A-BFD50179D6AC     2700



  Note: If you make a mistake while using gdisk, you can enter a controlC to exit without saving your changes.


Below is an example of the commands to enter into gdisk. What you need to enter may vary slightly.

GPT fdisk (gdisk) version 1.0.1

Partition table scan:
  MBR: protective
  BSD: not present
  APM: not present
  GPT: present

Found valid GPT with protective MBR; using GPT.

Command (? for help): t
Partition number (1-3): 2
Current type is 'Windows RE'
Hex code or GUID (L to show codes, Enter = 700): AF00
Changed type of partition to 'Apple HFS/HFS+'

Command (? for help): t
Partition number (1-3): 3
Current type is 'Windows RE'
Hex code or GUID (L to show codes, Enter = 700): AB00
Changed type of partition to 'Recovery HD'

Command (? for help): x

Expert command (? for help): a
Partition number (1-3): 3
Known attributes are:
0: system partition
1: hide from EFI
2: legacy BIOS bootable
60: read-only
62: hidden
63: do not automount

Attribute value is 0000000000000000. Set fields are:
  No fields set

Toggle which attribute field (0-63, 64 or &lt;Enter&gt; to exit): 49
Have enabled the 'Undefined bit #49' attribute.
Attribute value is 0002000000000000. Set fields are:
49 (Undefined bit #49)

Toggle which attribute field (0-63, 64 or &lt;Enter&gt; to exit):

Expert command (? for help): w

Final checks complete. About to write GPT data. THIS WILL OVERWRITE EXISTING
PARTITIONS!!

Do you want to proceed? (Y/N): y
OK; writing new GUID partition table (GPT) to \\.\PhysicalDrive1.
Disk synchronization succeeded! The computer should now use the new
partition table.
The operation has completed successfully.


The Mac firmware and El Capitan OS X operation system both rely on the GUID values in the GUID Partition Table (GPT) to aid in determining the format of a volume stored in a partition. Since the GPT contains the wrong GUID value for both partitions 2 and 3, you can not boot your Mac from either of these partitions.

The Windows 10 operating system is a little less restrictive. Windows 10 will look at the contents of a partition and try to determine format of the volume. Windows may do this even if the partition has the wrong GUID value in the GPT. This is why windows detects the HFS formatted "Macintosh HD" and "Recovery HD" volumes while the firmware used to boot the Mac does not.

The GUID of DE94BBA4-06D1-4D40-A16A-BFD50179D6AC represents a Windows Recovery Environment partition. Evidently, you do not have such a partition. When I install Windows 10 on my 2013 iMac, a partition of this  type was created. It is about 450 MB in size and followed after the 
Windows 10 partition. Other users have posted their installation of Windows 10 did not create this partition. So if you had this partition, it is possible EaseUS erased it. Anyway, you do not need a Windows Recovery Environment partition for normal use of Windows 10.