<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0607</schemaVersion>

    <documentType>3</documentType>

    <periodOfReport>2026-10-05</periodOfReport>

    <noSecuritiesOwned>0</noSecuritiesOwned>

    <issuer>
        <issuerCik>0002076561</issuerCik>
        <issuerName>Pine Tree Acquisition Corp.</issuerName>
        <issuerTradingSymbol>PAXG</issuerTradingSymbol>
        <issuerForeignTradingSymbol></issuerForeignTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0002104909</rptOwnerCik>
            <rptOwnerName>Pine Tree Sponsor Group, LLC</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerNonUSAddressFlag>false</rptOwnerNonUSAddressFlag>
            <rptOwnerStreet1>C/O PINE TREE ACQUISITION CORP.</rptOwnerStreet1>
            <rptOwnerStreet2>418 BROADWAY, #6538</rptOwnerStreet2>
            <rptOwnerCity>ALBANY</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>12207</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Class A Ordinary Shares</value>
                <footnoteId id="F1"/>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>135000</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <derivativeTable>
        <derivativeHolding>
            <securityTitle>
                <value>Class B Ordinary Shares</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>0</value>
            </conversionOrExercisePrice>
            <exerciseDate>
                <footnoteId id="F2"/>
            </exerciseDate>
            <expirationDate>
                <footnoteId id="F2"/>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Class A Ordinary Shares</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>4928571</value>
                    <footnoteId id="F3"/>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeHolding>
        <derivativeHolding>
            <securityTitle>
                <value>Rights</value>
                <footnoteId id="F4"/>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>0</value>
            </conversionOrExercisePrice>
            <exerciseDate>
                <footnoteId id="F5"/>
            </exerciseDate>
            <expirationDate>
                <footnoteId id="F5"/>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Class A Ordinary Shares</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>101250</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeHolding>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">Represents shares contained within units that the reporting person has irrevocably agreed to purchase at the closing of the Issuer's initial public offering (the &quot;IPO&quot;).</footnote>
        <footnote id="F2">The Class B ordinary shares of the Issuer are convertible into the Issuer's Class A ordinary  shares concurrently with or immediately following the consummation of an initial business combination, or earlier at the option of the holders thereof on a one-for-one basis, subject to the adjustments.  The Class B ordinary shares have no expiration date.</footnote>
        <footnote id="F3">Includes up to 642,857 shares which will be surrendered to the Issuer for no consideration after the closing of the Issuer's initial public offering depending on the extent to which the underwriter's over-allotment option is exercised.</footnote>
        <footnote id="F4">Represents rights contained within units that the reporting person has irrevocably agreed to purchase at the closing of the Issuer's IPO.</footnote>
        <footnote id="F5">Each right will convert automatically into three-fourths of one Class A Ordinary Share at the closing of an initial business combination by the Issuer.  The rights have no expiration date.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/s/ Pine Tree Sponsor Group, LLC by Pine Tree Top, LLC, Manager</signatureName>
        <signatureDate>2026-10-05</signatureDate>
    </ownerSignature>
</ownershipDocument>
